Shadows Problem

I had been running Windows XP 32-bit up until a couple days ago, and now that I've upgraded to Windows 7 64-bit I'm having various problems with games and other software. One of the bigger issues right now is that shadows look absolutely terrible in every game I've played (currently Borderlands, Shattered Horizon and Left 4 Dead). They look really blocky and grainy, especially when viewed up close. I never had this problem with XP.

I checked my graphics driver and it's up to date. The rest of the graphics seem to more or less be okay, as far as I can tell. I've checked to make sure that the shadows are turned up to full, and they are. Any ideas what's causing this or what I can do to try and fix it?