Have you tried changing the wireless channel to one that isn't being used by your neighbors?
Windows 7 wireless networks are more picky about over crowded channels than XP and will disconnect if the channel is overloaded. You can change the wireless channel in your routers set up page. You should also change to WPA-2 with AES encryption if you aren't doing that already.
In general, channels 1, 6 and 11 are the best channels to use.
The Xirrus wifi inspector software will help you figure out which channels are the least crowded in your area. Wi-Fi Inspector | Xirrus