Assuming you mean "prototyping" -- why not just use the Visual C# / VB ... themselves. It's pretty quick to put together mock screens w/ them.
It's for preparing functional specifications, so not quite prototyping, in fact it's more for functional proposals that I prepare to try to get contracts signed. I guess I can put in the extra effort of making the wireframes using Visual Studio but no body's
going to pay me for it so I try to keep this stage as short as possible.