Very similar problem. I have a Mac that I use bootcamp to install windows xp. I'm able to connect to my wireless network, but every couple of minutes (haven't calc if there is pattern) my internet connection dies. Though I'm still connected to the wireless network.
I have a hunch that it's the wireless drivers but I have no proof and no solution. A while back I had thought I read other people had the same problem with mac's wireless connection in windows,but I'm not sure.