I had a Sempron PC under my desk angled next to my G5 with Airport Antennae.
The AE was losing signal like a mad dog and generally misbehaving. I never lost a signal on my QS2K2 when I had a Linksys Bridge hooked to it and parked next to the PC
I moved the PC to a remote corner of the house and voila! The AE card/antennae mix performs fantastically with no dropped signal.
Go figure.