Run Hijackthis and select "Do a system scan only", place a check by the following entries.
O4 - HKLM\..\Run: [sp2update] C:\windows\sp2update00.exe
Close all open windows and browsers, and hit "Fix Checked".
Find and delete this file (you might need to see hidden files).
C:\windows\
sp2update00.exe
Download Ewido.
http://download.ewido.net/ewido-setup.exe
Install and update it, then run a full scan and remove all it finds.
Then reboot and post a new Hijackthis log.