I've scoured the graphics issues everyone's been having, but none of them seem to resemble what's going on on my computer. I recently upgraded my video card from integrated to an ATI Radeon HD 2400 PRO. Then I switched from my small flat screen monitor to a larger one to support a higher resolution.
So I got it running, and I install all the software and drivers for it, but when I go to play, the game suddenly fails to render the majority of the graphics, like so:

Granted, it runs 10 times smoother than my integrated, but what good is it when I can't even see what's going on?
Even on my integrated video card, this was never an issue. I installed DirectX 10 to see if this would solve the problem, but it hasn't. Neither has tracking down updated drivers, reinstalling Guild Wars, or fooling around with the resolution.
I'm using Windows XP SP1 right now. Any help or guidance would be really appreciated.