I have seen silmliar issues on some of the older BT Homehubs with XP machines. The laptops would connect to other wireless networks, but not the main one, even though other PC's could succesfully connect.
In these cases I restored the routers back too their defaults as rebooting them was not enough to solve the problem. I think your next step is to try and connect to an alternative wireless network. I always carry a small netgear wireless router for testing this type of thing.
Are you using the windows wireless management tools, or a third party application to manage the wireless connections?