I've got a 12" alum powerbook and have had the chance to use both the airport extreme with airport express as a bridge, and a Linksys WRT54G router.
I own a WRT54G with one factory and one omnidirectional antenna and use the hacked firmware Alchemy-pre5.1 2.07 with it and the range is amazing, great speeds at 200 feet away. Do a google search for "WRT54G hacked firmware" and you'll find a few different packages. Basically, it lets you output 900X the power than the factory settings. Instead of outputting only 28mw of power it lets you output 251mw of power, at least tripling your range. I can be anywhere in the house and far in the back yard (half an acre) and still get a great reception. The factory settings are terrrible, but if you use the hacked firmware you'll see your distance at least triple.
I've also used an airport extreme with an airport express briging the connection, and the range of those two put together is equally impressive. Easily a 300 foot range, slightly farther than the Linksys. The airport base station and airport express was easier to set up, although I have no complaints about the linksys.
The difference is the price, you can get a WRT54G for about $75 and an omnidirectional antenna for about $30, but you'll pay well over $300 for the airport extreme and express combo.
If you need a print server and airtunes, then get the airport extreme and express combo. If you just need wireless internet get the WRT54G. If you want your internet to go far but don't need it in every direction, get an unidirectional antenna.
If you have a WRT54G and want to dramatically increase your range, go here
http://wrt54g.streamfire.net/
and download the new firmware, go to your router settings (usually at
http://192.168.1.1) and go to Administration, Firmware Upgrade. It takes about a minute to install and you may have to grab the original CD and run the setup to get the internet connection working - but basically it unlocks all sorts of settings that you normally don't have access to. Under the "wireless/advanced settings" tab you'll see a new drop down menu called Xmit power, which lets you give out 900 times more power than usual. It gives you an incredible amount of range... There are other settings to that i'm sure you can mess with, but if you just increase the power you'll see a huge increase if your distance.
My only issue with my Linksys is that whenever anyone calls and I pick up using the cordless phone the internet connection falls out. I don't know if this does it with the airport base station, but it does on the linksys. I'm using channel 6 on the router and channel 11 on the phone, so they shouldn't interfere - but they do.
crackrock