>I dropped a TabControl on a form and I see it is not transparent. My form background is dark. So, I can see that the upper right part of the TabControl is not transparent. Is there a way to do it?

Have you looked at the "Giving Your Control a Transparent Background" help topic?

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon/html/vbtskgivingyourcontroltransparentbackground.asp