As far as I know, only a form can be an MDI container. What version are you using, though - I speak from a VB6 perspective, and may be behind the times on this.
As to what you could do instead, there are a myriad of ways you can design a user interface. Perhaps you could provide some more detail on what you're trying to accomplish?
I am using Visual Basic 2008 beta 2
I Started using vb6 myself but now vb 08 beta 2.
I can say there isn't much of a difference except for the language has changed a tid bit.
I am making a halo modding application. I'm sure you have heard of halo.
I have a tab control as a menu strip and I have several different editors that need to be displayed when clicked. I can't have the normal MDI container on the form because it interferes with the tab control.
If you have any suggestions I would be very open minded.
Thanks for the reply.