Actually, it is VB6, and the full source is available here:
www.Javin-Inc.com/Tron.zipAs for the dimensions of the gui, shoot for 1024x768, and when I put it on the screen, it'll be sized appropriately for each resolution. As for what it actually needs to display, you take a look at the game and tell me. I know for one it'll need a small map in one of the corners to show the positions of other bikes, plus your typical GUIs to set your graphics settings, difficulty, ip connections (host/client) etc.
-Javin