I see this thread being confused by the bit/byte conundrum:
Communication speeds are almost always quoted in bits (i.e. a 0 or 1) per second. (To make them sound LARGER!) - This makes sense. (You are told how many "0"s or "1"s the thing can chuck out/recieve in a second.)
However; your computer will tell you download speed in bytes per second, as a byte is the smallest amount of useful data a computer can handle.
A byte is a string of 8 bits i.e. 00110010.
This is why your 54kbps (kilo-bits per second) actually gives you download speeds of roughly 10x less (best I've got is sort of 8 kilo-bytes. (Also because a kilobyte is actually 1024 bytes, not 1000 bits like a kilobit)
So getting back to it:
I have a iMac (G4) with an airport express card in it and a PowerBook G3 (Pismo) with a Linksys 802.11b card inside. (also does "g" but the slot in this old machine can't handle the bandwidth)
I have the iMac running a airport network to the PB, sharing files, internet and printers.
For example:
I just transfered a 24 MB file in 12 seconds on a "b" network - I get that as 2 mega-bytes per second, but you could get faster.
The upshot of all this:
If you want to primarily use your airport card to share the internet 802.11b is likely to be as fast as you'll ever need. If you are going to want to connect to other computers and transfer around GBs of documents, b will not be fast enough, but wirelessly it's the best the old iBooks can do! - making this whole thing a bit moot.
As you can see from my example you could transfer a large file (~100MB) in a minute or less, which I find fine for 95% of the time. In the rare occasion that I may need to transfer a file lager than, say, 250MB, I'd pull the crossover cable out, although the time it takes to do that and configure a temporary local wired network would probably be longer that I would save just using 802.11b!
A special case:
If you use your computer a lot for video editing, 802.11b (or standard "Airport") will most likely not have the bandwidth to stream your iMovie (or other) project to your remote laptop.
Also, 802.11b will not be fast enough to stream audio to an airport express-connected Hi-fi. (You need a "g" network, as stated somewhere in the Apple sites.)
Also note:
All speeds are likely to increase if you set up a proper wireless network using, say, an airport express or extreme base station.
