What IP is it giving you? I don't think your computer is able to release/renew your external IP address using command prompt, that must be done by your routers control page.

PS. Comcast IPs are...

You can't reinstall without A disk, but it doesn't have to be YOUR disk, if you have a friend with a windows disk it should work as long as it's the same version (should be the OEM version). Be very...

There are CD bootable versions of XP available, but their legality is questionable at best, but google it if you're interested.

You can use a CD bootable Linux distrobution as salim suggested...