Sir, please read this:- http://www.techenclave.com/pc-peripherals/notice-all-those-who-need-help-138633.html
...And then, get an HD 4670
PS: What resolution do you game at and what PSU is currently in use? If its a generic one, then i won't recommend getting a new GPU till you change it, even if it is a frugal one like the aforementioned.