HijackThis usually works quite well for those kinds of things...It lists all the current programs/registry values running, you can then select individual parts and delete them. You can also save a log and post it here if need be.
There should be a section like this:
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page =
http://www.google.caR1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL =
http://www.mdg.caR1 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page_bak =
http://www.google.ca/R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Window Title = Microsoft Internet Explorer provided by Sympatico
Which is where the problem will most likely be...