uhmm...it's been a long time since I messed around with this.
Here's what I did:
where kWindowWidth and height are the width and height of what you're about to copy. IIRC this leaves you with myBMP
HDC myDC = CreateCompatibleDC(originalDC);
HBITMAP myBMP = CreateCompatibleBitmap(myHDC);
containing what you want.
This is just out of the back of my head but these functions
(possibly in conjunction with some others) will do the trick.
So look them up at MSDN and I hope you'll be set .
If this don't work for ya let me know and I'll find out exactly what I did.