Service Pack 2 / acquiring network address

[Shatter]

I am having an issue with service pack 2 and my network connection. I am not using wireless, and I have a router with Comcast for my ISP. What happens is one computer of my 3 after I had Comcast installed kept hanging on acquiring network address and the other 2 work fine. After trying 2 ethernet cards, plugging directly into the modem(no router) and many other fixes, I re-installed windows xp. Now, I found the problem but still cant fix it. After I re-installed XP the network was fixed, worked great on the bad computer. Soon as I downloaded and installed Service pack 2, it went back to the acquiring network address problem. So I did system restore back to before I put SP2 on and again it worked fine, so I know its SP2 thats my problem. I already downloaded and installed the Windows "fix" for SP2 and it is not fixing the issue and I do not know what else it is I can try. Any suggestions?

[Sonic]

What encryption used on the wireless network ?

You can try to install windows with a CD with SP2 splitstreamed. Ask a CD of friend to test.