I have two desktops. One in the basement and one on the second floor of my house. The modem is in the basement and I cant run a cable down to it from upstairs. Neither desktop has a wireless card. I have this shitty belkin router that has this attachment htat is supposed to make a desktop wireless but it doesn't work because my ISP rejects it when it tries to connect. I really have no idea what options I have. My ISP wont give me another modem for upstairs. What can I do?

http://www.google.com/products/catalog?q=PowerLine+adapters,&ie=utf-8&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&cid=3418660565776631015&sa=X&oi=product_catalog_result&resnum=3&ct=result#ps-sellers

http://tinyurl.com/883luq

Use powerline adapters. It will use the electrical outlets and your homes electrical wiring to connect the modem to the upstairs comp. They were buggy when they first were released but that is said to have been remedied since then.

^Good advice, the ethernet over power stuff has definately improved over the last few years. But that doesnt solve the sharing problem. It sounds like your ISP is locked in on the MAC on your PC, since when you added a router it failed to connect to WAN. If your router has a MAC address clone feature use that to spoof the mac of your directly connected PC, could save you a phone call to your ISP to reset whatever mac lock they have. Also, if your computer has a second ethernet port you could basically keep your current working config, but with the second computer set up with a network bridge in winxp to bridge the two adapters.