First of all, this is unrelated to user controls, so a new topic would have been appropriate instead of continueing an old one.
Secondly, this is an html / css question, not related to asp.net, so another forum category would have been appropriate as well.
Thirdly, Google gives you this answer in a split second.
Finally, I wouldn't try to do this. I hate sites that do it. The scrollbar belongs to the user's browser / OS and not to the web site.