There are at least 2 places that you will need to delete the URL from:
1. run regedit and look for
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\TypedURLs (I counted that the last 25 URLs are possiblly stored here)
2. your history
click on history and look for the url in the left frame and delete it (you may have to possibly look several times if the url has been accessed
several times in the past).
3. ..... someone else can fill in 3, 4, ...
Good luck