A some free tools to remove spyware, undo browswer hijacking, and stop popups are:

AdAware - by Lavasoft
http://www.lavasoft.de/
This one is really easy to use and only seems to identify known spyware. It also backs up the data it rips out of your system.

HijackThis
http://www.tomcoyote.org/hjt/
HijackThis is not as easy as AdAware. I identifies everything that is hooking your browser and then you have to sift through the list and select what you want to kill.

EmeraldPopStop
http://www.EmeraldPopStop.com
Kills popups and Windows Messenger Service dialog box popups. (Not to be confused with MSN.)


PSA - None of this will replace a good anti-virus program or regular backups. :-)