First off, I only want to provide my experience here so that others will have less trouble than I.
Hardware: Two Blue & White G3's running 10.4.6 and 10.4.6 Server.
Summary: I purchased a Belkin PCI NIC model F5D7000 (version 4.00), popped it in the Mac and immediately it was recognized as an Airport card with no problems.
The story doesn't end here because according to the bulk of online information, the F5D7000 uses the Broadcom chipset and works the same as an Airport Extreme card. I only later found out that this is an over-simplification and the version of this card is very critical. I only got lucky as there are now six versions of this card floating around out there. Not even Belkin Tech support can tell them apart.
I needed to purchase a second one for my other Mac and this is where my aggravation really begins. I was faced with version 4.00 and 5.00 on the shelf. I only selected the 5.00 because it was newer and had a removable antenna where the 4.00 does not. This was a huge mistake as the 5.00 does not work as an Airport Extreme card at all... I could not get it to work... I exchanged it for a version 3.00 and subsequently purchased a version 2.00.
Results:
Let me summarize my test results below.
v1.00 - Untested but have read that this version contains the Broadcom chipset and works as an Airport card.
v2.00 - Airport Confirmed with Broadcom chipset.
Belkin told me this version was not Mac compatible.
v3.00 - RT2500 chipset and not recognized as an Airport card. However I did get it working with the 11g-RT2500 Drivers provided at this link- http://www.ralinktech.com/supp-1.htm -> Even though Belkin's F5D7000 product page mentions Mac compatibility, version 3.00 is the only supported card and that's only with OS 10.2 and 10.3. Belkin's drivers do NOT work in Tiger and Tech support will not assist you with Tiger.
v4.00 - Airport Confirmed with Broadcom chipset.
Also note, as far as I could tell, this is the only version without a SMA type removable antenna. Permanent mount that is upside down while in a PowerMac. Easily flipped 180 with some basic tools.
v5.00 - I can only confirm that this version did NOT work as an Airport card. It may have the same RT chipset and work with the same RT drivers as the 3.00, but I did NOT figure out or confirm this before returning it to the store.
v6.00 - ?? unknown. Some stores carry this version but I did not get my hands on one.
Conclusion: I think this is a great inexpensive card but it's definitely in a gray area between Mac unsupported and fully supported. Belkin needs to decide which way to go and correct their online documentation and tech support people.
If you can get your hands on a version 1.00, 2.00, or 4.00, you'll probably be ok with a great card you can setup as an Airport card in under a minute. With version 3.00 (and maybe 5.00 & 6.00), you'll need to do a little more work installing the RT drivers. Actually, setting that up was very easy too but since it's not recognized as Airport, you have to make sure to do the extra configurations so you automatically connect on start-up.
If you get a Belkin F5D7000 that has neither the Broadcom or RT chipsets, then you are outside of my testing arena and I can't really say if/how that would work in a Mac.
Other Comments: The most difficult part was finding comprehensive online information about this card, chipsets, versions, and Mac support. Also if you get a RT chipset, the Mac initially will not even see this PCI card, therefore, finding out what chipset you have is virtually impossible. Anyone with a Windows PC handy can install it in there perhaps to find out more details.
I hope that some people will find my post somewhat helpful. I know I was dying to find a post like this about 24 hours ago.

UPDATE: User on another forum has confirmed that his version 5.00 requires the RT2500 drivers from Ralinktech confirming my suspicions that this card uses the RT2500 just like the version 3.00.
Now it would not surprise me to find out version 6.00 is using the Broadcom chipset if we can trust the "sort-of-leap-frogging" pattern here. Anyone using a version 6.00 yet on a Mac?
UPDATE #2: It seems that once you get above a version 4.00, nothing works with Tiger. It was confirmed that version 6.00 has an RA Link chipset, however it's different than the version 3.00 and nobody has been able to get the RA Link drivers working under Tiger for this card. Version 5.00 has an Atheros chipset and I know of no drivers for that.
If you have a version 5.00 and above, I think you're out of luck and will have to get your hands on something older.
Versions 1.00, 2.00, or 4.00 will work as Airport out of the box. Also in a pinch version 3.00 will work but you'll need the third party software and drivers from RA Link.
Hardware: Two Blue & White G3's running 10.4.6 and 10.4.6 Server.
Summary: I purchased a Belkin PCI NIC model F5D7000 (version 4.00), popped it in the Mac and immediately it was recognized as an Airport card with no problems.
The story doesn't end here because according to the bulk of online information, the F5D7000 uses the Broadcom chipset and works the same as an Airport Extreme card. I only later found out that this is an over-simplification and the version of this card is very critical. I only got lucky as there are now six versions of this card floating around out there. Not even Belkin Tech support can tell them apart.
I needed to purchase a second one for my other Mac and this is where my aggravation really begins. I was faced with version 4.00 and 5.00 on the shelf. I only selected the 5.00 because it was newer and had a removable antenna where the 4.00 does not. This was a huge mistake as the 5.00 does not work as an Airport Extreme card at all... I could not get it to work... I exchanged it for a version 3.00 and subsequently purchased a version 2.00.
Results:
Let me summarize my test results below.
v1.00 - Untested but have read that this version contains the Broadcom chipset and works as an Airport card.
v2.00 - Airport Confirmed with Broadcom chipset.
v3.00 - RT2500 chipset and not recognized as an Airport card. However I did get it working with the 11g-RT2500 Drivers provided at this link- http://www.ralinktech.com/supp-1.htm -> Even though Belkin's F5D7000 product page mentions Mac compatibility, version 3.00 is the only supported card and that's only with OS 10.2 and 10.3. Belkin's drivers do NOT work in Tiger and Tech support will not assist you with Tiger.
v4.00 - Airport Confirmed with Broadcom chipset.
v5.00 - I can only confirm that this version did NOT work as an Airport card. It may have the same RT chipset and work with the same RT drivers as the 3.00, but I did NOT figure out or confirm this before returning it to the store.
v6.00 - ?? unknown. Some stores carry this version but I did not get my hands on one.
Conclusion: I think this is a great inexpensive card but it's definitely in a gray area between Mac unsupported and fully supported. Belkin needs to decide which way to go and correct their online documentation and tech support people.
If you can get your hands on a version 1.00, 2.00, or 4.00, you'll probably be ok with a great card you can setup as an Airport card in under a minute. With version 3.00 (and maybe 5.00 & 6.00), you'll need to do a little more work installing the RT drivers. Actually, setting that up was very easy too but since it's not recognized as Airport, you have to make sure to do the extra configurations so you automatically connect on start-up.
If you get a Belkin F5D7000 that has neither the Broadcom or RT chipsets, then you are outside of my testing arena and I can't really say if/how that would work in a Mac.
Other Comments: The most difficult part was finding comprehensive online information about this card, chipsets, versions, and Mac support. Also if you get a RT chipset, the Mac initially will not even see this PCI card, therefore, finding out what chipset you have is virtually impossible. Anyone with a Windows PC handy can install it in there perhaps to find out more details.
I hope that some people will find my post somewhat helpful. I know I was dying to find a post like this about 24 hours ago.
UPDATE: User on another forum has confirmed that his version 5.00 requires the RT2500 drivers from Ralinktech confirming my suspicions that this card uses the RT2500 just like the version 3.00.
Now it would not surprise me to find out version 6.00 is using the Broadcom chipset if we can trust the "sort-of-leap-frogging" pattern here. Anyone using a version 6.00 yet on a Mac?
UPDATE #2: It seems that once you get above a version 4.00, nothing works with Tiger. It was confirmed that version 6.00 has an RA Link chipset, however it's different than the version 3.00 and nobody has been able to get the RA Link drivers working under Tiger for this card. Version 5.00 has an Atheros chipset and I know of no drivers for that.
If you have a version 5.00 and above, I think you're out of luck and will have to get your hands on something older.
Versions 1.00, 2.00, or 4.00 will work as Airport out of the box. Also in a pinch version 3.00 will work but you'll need the third party software and drivers from RA Link.