What you need:
1 X 17" LCD monitor (any size will do, i have some lying around..)
2 X meters of black sticky paper (for covering the desk + the lcd bezel, Iv'e thought of all the posiblities: glass, perspex, acrylic - this is the ceapest!)
1 X DVI/VGA connector (i got 5 meter for $7)
!! Update: I added touch sensitivity via Wiimote and IR-pen. visit: http://www.wiimoteproject.com/index.php?action=downloads;cat=3 to download files and try it for yourself!
Step 1: Cutting the border out of the wooden desk
Then use a pencel to mark the outer border and make 4 holes with a drill saw. I found that is the best and easiest way to cut a rectangle in a piece of wood.
finish the edges with a sander.