Uninstall everything but the operating system and a few trusted programs. Back it up - create a restore point.
Use the registry editor (regedit.exe). Look in HKEY_LOCAL_MACHINE in the SOFTWARE folder and in the HKEY_CURRENT_USER SOFTWARE folder. Delete any subfolder that is for software you uninstalled.
Look in the remaining subfolders and use Google to identify the entries. Keep it if it is for software you trust. Otherwise, delete it. You will eventually find a search engine hidden in the registry. Delete it. Create a restore point. Reboot.
If successful, test for the hijacker. If it is gone, reinstall all of the software you want.
It took me a weekend, but it saved me $100 Norton wanted to charge me for them to do it. I made alot of mistakes, including deleting a bunch of drivers. That’s OK because I found an installed updated drivers and my machine works much better.
Actually I have Vista, so I am not sure this sledgehammer to kill a gnat method will work for Windows 7.