Cannot uninstall SP2 for XP

Hello

I just upgraded my computer from XP sp2 to SP 3 and now at home I cannot connect to my Xbox 360 or to a wireless network I can usually pick up.
Mainly I use my laptop connected via ethernet cable directly to my Xbox 360. I then set my Nic IP to 192.168.0.1 and the 360 to 192.168.0.2 and it ALWAYS worked. Then I installed SP3 and now my 360 will not recognize my computer and the wireless will connect to the network I use but I dont have a actual connection. It shows connected but going to any website or signing into MSN doesnt work what so ever. I can however get online if I have a STRONG wireless signal. But if its a low or very low signal I connect but cannot actually use the internet.

Do you have to have the original SP3 installer to uninstall? When i try it says it cannot find file.

I use the 360 to laptop connection for streaming video and music files through my tv/surround sound.
PLEASE HELP!!!!