Wireless connection dying, nearby PCs unaffected?

I have a 2.8 gig intel quad-core Mac Pro with system 10.5.2, and a 1.5 gig Powerbook G4 (system 10.3.9). They are set up in the same room as a PC (don't know the configuration, it belongs to a co-worker), with the powerbook being about five feet from it on the other side of the table, and the tower on the other side of the room, behind a low wall. Our Linksys router, connected to a Motorola cable modem, on the Comcast network, is in the next room over.

Frequently, the Macs will lose internet access. The Airport icon in the menubar shows only a tiny dot of signal or nothing at all, and no connection can be made to the web or other applications. The PC is completely unaffected, and continues to surf and download without a problem.

The only way we've found to get the connection back is to shut off (unplug) the router for a few seconds, plug it back in, and then turn Airport off and back on on the two Macs. This usually gets us connectivity back... for a while.

None of us have any idea what's going on. My only guess is maybe the router is gradually losing signal strength, and the PC is sensitive enough to continue to pick it up while the Macs aren't? Beats the heck out of me, all I know is it's an amazing pain in the neck.

Anyone have any insights to what's going on here, and what I can do to fix it? Please?