OK, I tried taking screenshots but they all look fine on the desktop. so i used MSPaint to show what I see in-game.
This is torus trooper, it only runs at 640:480 and this is what the screenshot looks like:
This is what i actually see when i run the game:
The BIOS splash screen and the XP load screen are also cut off like this so i assume it's specific to the 640 by 480 resolution.
This is the HL2 screenshot: (at 1280x1024, my resolution before i switched monitors)
This is what I actually see at 1280x1024:
The weird thing is another game (operation flashpoint) runs fine at 1280x1024.
After a lot of random clicking i managed to drag the HL2 options menu to the corner of the screen, and set it to the right aspect ratio, but it's still screwed up:
I don't have a digital camera so the MSPaint mockups are about the best i can do, if anyone wants more pics I will put them up.