Looking to buy my mate a gfx card..

hey all, looking to buy my mate a gfx card to try and get him into pc gaming without breaking the bank, which would be wasted anyway cos he has a relatively low end computer. well its old lol. I believe its from 2008, the details are a little sketchy as he has no idea about computers and i just had a quick look at it, wat i do know is that the motherboard is a DG33M06 and he has only got a 300 watt psu , 4 gig of ram , running vista 32 bit. i believe the cpu is just a dual core? not sure on the cpu to be honest but pretty sure thats what they were selling at office works at the time lol. he paid like 900 bucks at the time so safe to say he got ripped off, just wondering if i buy him a 7750 would that be of any benefit? will the cpu etc be so crap that its pointless is my main concern? Im pretty sure there arent any compatibility issues, i saw the pcie slot so all should be good. the power supply is obviously another concern but i think the 7750 only uses 64 watts? and last but not least will he be able to play games on it anyway lol, like say battlefield 3 on low to medium settings? any advice/ guesses would be great thanks.