Steve,
If you see a message like that again (after you get this cleared up), do not click on it. Use the Alt key and the F4 key together to close that window.

In the settings for your browser, you will have a field in which to indicate your home page URL. Find that and click on the field. If there is only one URL there, you can probably delete it (highlight it then use Backspace key) and type in the URL of the page you want as a homepage. In the version of Internet Explorer I use, it's found in the Tools drop down menu, in the Internet Options window. If you are using a different browser, try a search for "homepage" in the "Help" file.

If you find multiple URL's in the field in which to indicate your home page URL, you have a trojan and will have to remove it.

Good luck!
rags