Sounds like a Browser Hijack.
In my experience, they tend to keep themselves hidden from your first line of freeware defense: Spybot Search & Destroy, AVG Antivirus, and Ad Aware.
Online scanners are also out of the question, given the nature of the problem, but doesn't hurt to try. One way around the search engine redirect is to open the Cache'd version of the website instead. But sadly, once you click on another link within that website you'll be redirected again. What has worked for me in the past are Malwarebyte and SuperAnti Spyware run in Safemode. Only once had to resort to the HijackThis! and Killbox combo, with an educated guess via Process Library and fingers crossed.
This is the list Gryphonstalker likes to post occasionally.
AVG - http://free.grisoft.com/
Housecall - http://housecall.trendmicro.com/
SuperAnti Spyware - http://www.superantispyware.com/
Malwarebyte - http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html
Ad-Aware - http://www.lavasoftusa.com/
(Green button on your right.)
Spybot: Search & Destroy - http://www.safer-networking.org/en/index.html
Spyware Blaster - http://www.javacoolsoftware.com/spywareblaster.html
(This is a preventive proggie, just update.)
Spyware Guard (Beta) - http://www.javacoolsoftware.com/spywareguard.html
(This is a preventive proggie.)
JKDefrag - http://www.kessels.com/JkDefrag/
(disk defragmenter and optimizer for Windows 2000/2003/XP/Vista/X64.)
PC Wizard 2008 - http://www.cpuid.com/pcwizard.php
(Utility designed to analyze and benchmark your computer system.)
Advanced Windows Care Personal - http://www.iobit.com/
(helps protect, optimize, and repair your computer.)
CCleaner - http://www.ccleaner.com/
(system optimization and privacy tool.)
Answers That Work: Task List Programs - http://www.answersthatwork.com/Tasklist_pages/tasklist.htm
(This site has a pretty comprehensive list of processes.)
Process Library - http://www.processlibrary.com/
KillBox - http://www.killbox.net/
(Use at your own RISK: a tool to delete in-use files. http://killbox.net/help.html)
- last resort to really nasty viruses masquerading as essential window files; Do your research first!!! Edited, Jan 26th 2009 7:35pm by Zemzelette Edited, Jan 26th 2009 7:39pm by Zemzelette