Airport problems

I'm in the same boat and can't figure it out. I have a 1st gen MacBook that works flawlessly with my new Airport Express. I installed a new 802.11n card in my Mac Pro. At first I get full bars, but as soon as I hop on the internet, it drops to 2 and nothing loads. I have to reboot to get full bars back. It'll be good for a bit, but will then drop out again. The AE is about 20' away. The MacBook works all the way out to the end of my driveway w/o dropping a single bar. So it can't be a reception thing. It must be the Mac Pro. I hope the 10.5.3 update fixes it.

I can relate, since I've taken my BlackBook to campus and I get great WiFi connection with Full Bars at the beginning, then I walk about 15 feet away and "poof" no bars. I've ended up switching to another campus WiFi ID and the problem seems to have gone away. It's still frustrating because there seems to be no "fix" in the near future, since my IT people say it's not on their end.