Look what I found a patch from Microsoft. Apparently an invalid IP can also be caused from limited connectivity and there is a bug in the SP2 pack that can cause it. I've learned something new.

Anyway here is the link with directions on how to fix it. Maybe this is where you should start first.
http://www.pchell.com/support/limitedconnectivity.shtmlthen try this if the patch doesn't work after reboot:
Unplug your DSL and Router if you have one from both the wall and jack.
Wait 2 minutes
Plug in the dsl box, after all lights are on other than ethernet if your using a wireless router, plug back in the router.
If your not using a router, just let it refresh and then try the site again.
Seems to me an ipconfig/release/renew would work just as well. I'll wait till I hear something from you if either of these things worked. If not I'll search some more.