I haven't done this myself but try these idea's...
1. Use the .NET events KeyDown, KeyUp to see what button has been pressed
and if it is Print Screen (I believe the keycode is 44, but best check) see
if you can find a way of cancelling it - though I'm not sure if you can do it
like this.
2. You can hook into the Windows messages so you can trap the key stroke and
bin it before your form gets it.