So I've had this pretty decent PC for a while and haven't done much w/ it. It's a dell xps 8300. The saving grace here is the 16gb of ram and a i7 cpu. It has a dumpy vid card (radeon 6450) and I bet if I upgraded that I'd be gravy. Trouble is I know nothing about videocards and even what I can put in my machine. I'm pretty sure my power supply is 480w. Since dell makes their own boards it's hard to tell what exactly I have on board.
Any advice on a card? Will I have to upgrade my power source? I'd like to be able to play witcher 1, 2 on this as well as stuff like starcraft 2