[JAMF]

seems to me that it might be RAM-related, after all. if i look in my computer properties, it shows memory as: 4GB (3GB useable)

That means you are running 4GB on a 32Bit OS. WindowsX32Bit, Vista32Bit and Windows7 32Bit all have an addressable memory limit. You've put 4GB of memory in the system, but a 32Bit OS is only able to create addresses for around 3.5GB of it. So you've added a graphics card that requires it's share of addresses and takes what it needs. If you have 512MB on the card, you have 3GB of memory left for your other resources, like games and the like..

Downside to 32Bit: Memory... Downside to 64Bit: Drivers for older HW... No clue how that "XP in Windows7" option works with older HW. I suspect it makes software run in a virtual XP, but uses Win7 for the hardware and therefore it's drivers.