Hi
There are several ways to do this, personally I'd use the Windows API 'bitblit' function & appropriate DC's to actually transfer the desktop to a picture control or image control. I use this basic approach with my self written slide presentation software where it offers a neat solution and is very quick too.
I found some very good code that does screen capture exactly this way - written by Randy Birch and generously allowing free use in other apps - but it is not permissable to post the code elsewhere on the web which of course posting it here would be doing.
e-mail me and I'll send you the code - I'm sure you could find other ways but this code definitely works nicely so why re-invent the wheel.

Al (MaDbRiT)