es2daniel:
As Patio said, when you reinstall Windows, you start over from scratch.
This also include any components on your computer that didn't come with it initially (like drivers for your network card). If the drivers aren't installed, you're not getting on the net.
So...
Start -> Control Panel -> System -> Hardware Tab -> Device Manager button -> do you see any red X's, yellow !'s, or yellow ?'s?