After I had this problem for a while at my old house, I borrowed an external network adapter from a friend- it worked a lot better than the internal card my laptop came with. Then I moved and I haven't had any problems with it whatsoever, so my guess is that a combination of a cruddy Dell internal network card and lots of ductwork and other interference in my last house probably caused most of the problems.
Anyway, at this point I would recommend trying some different locations for the router to see if something isn't interfering with the signal.
I would also check to see if Belkin has released any new firmware for your router. I remember that Servpac2 introduced all sorts of security issues that were bumping computers off their networks, especially when the Windows networking software would do its thing and check for networks. That was a while back, but maybe there are new problems; it could be that by updating your firmware, you may resolve the issue. I think you can start from here.