Is there a "stay-alive" feature on the 2wire? How many DHCP addresses is it handing out? Does it report there is an IP conflict? do you have a linksys or something similar you could put in front of it to be the WAP?
On the machines themselves, are you using the wireless utility that came with the machine, such as Intel Pro? If so, have you tried "let windows manage my wireless settings"?
When it does stop, can you go start-->run-->services.msc
See if the wireless zero configuration utility service has stopped. This is a common conflict if you're running a third party wireless provider.