How about this one?

Briefly, the setup:
I have a small "home theater" HTPC in the living room, and a gaming PC upstairs that I also use for general web browsing. Wireless G router (WEP 128bit) makes the connection between them. Both PC's running XP Pro. Both PC's completely updated via the MS website, and even the router firmware is updated. My cable internet connection comes into the house -> into a Motorola modem -> into the Microsoft branded wireless router -> split into the computers (the HTPC is connected with CAT5, the upstairs runs wirelessly).

The Problem:
The PC upstairs can not sustain a connection to "the internet" - web pages and such I can get online right after the PC is booted up as would be “normal”, but it only last for a few minutes - I haven't figured out exactly how long or what (if any) event leads up to it. Suddenly the the connection breaks and I can't get online again unless I reboot. What's more unusual is that I can get e-mail as long as I wish! Ditto for swapping files and communicating with the other (the HTPC) downstairs. If I get online from the PC downstairs, it also stays connected indefinitely. So the connection to the router stays strong, and I know the cable modem connection stays strong too. But after a couple of minutes from being booted, the specific event of connecting to the internet from the PC upstairs stops.

Any ideas at all?