I had this same problem other week, my mates rang me and said why do i keep sending them emails about weird stuff. I changed my password and it seemed to work
well its hard to say without you knowing your motherboard but ifs its a recent PC in the last 2 - 3 years then it probably has a PCI express slot. I would=have a look in your PC first though. for $200 i would say either a GTX 460 1GB or a ATI HD 6850 1GB