You can try installing Lavasoft's AdAware software. This sounds like a form of add ware, and they may be able to help you remove it.
The site is www.lavasoftusa.com
If you are running W98 or later, you can use msconfig (type msconfig in the runbox) to check for and disable programs that run at startup.
I also saw a program to prevent web sites from changing your home page. I think it was in the download of the day section of www.emazing.com
Searching and editing the registry is notfor everyone. WARNING!!! IMPROPER REGISTRY EDITING CAN DISABLE YOUR COMPUTER!!! PROCEEDE WITH CAUTION. IT IS A GOOD IDEA TO BACK UP THE REGISTRY BEFROE EDITING IT.
To check for the program in the registry, open regedit (run box).
Use the search function in the edit menu. Search for runonce
When search finds a runonce look up the tree, and see what is in the run, runonce, and runonceexcept branches.
If you find something that looks suspect, copy down the exact wording of the key. You should be able to safely delete the key. At worst, you will disable a program, and need to re-install it, or add the key back in.
I would also search for the name of the website, and delete any references to it from the registry.
After you exit regedit, search for the program file that was called by the registry key.
If you are certian that this is the program that causes the problem, you can delete it.
If you are not sure, just move it to another folder.
Boot and see if the problem iscorrected, and that you have no new problems.