Also my system is a Dell Inspiron 531 with a AMD Athlon 64 X2 Dual Core Processor 4400+ (2 CPUs), ~2.3GHz.
If you need to know anything else just let me know. Price range $50-$70.
Here is what I found doing my own research, though the minimum says 400w, http://www.newegg.com/Product/Product.aspx?Item=N82E168...
That card is fine on that PSU as it dosent need any extra power cables and gets all its power from the PCIE slot. Dell PSU's are good quality units as well so you have no worries.
Basically if it dosent need a PCIE cable its fine.
A HD 5670 would be about the best card that dosent need a power cable (Check this as Axle made a version that did) at that price range.
I would be a bit more cautious as these pci-e x16 slots usually don't support 2.1 cards especially since it is from a oem. The card probably won't work due to the face of how old the board is and little to no updates from dell for the board.
Actually thats the cheapest 5670 I could find at newegg.Unfortunitly it only has 512mb of RAM which wouldn't be good if you plan on using a 1080p monitor.
You could get a 5570 for about $60 but you definitly won't be able to game with it.It's just a whole lot better than the on-board graphics.
I don't plan on playing games that are too graphically intense. And also, I don't want to play on max settings, I'd just like to play in HD with 60 FPS on about med-low settings. Right now I'm very into League Of Legends, and I play on completely bottomed out settings and in windowed mode and barely hold 30 FPS. It lags during intense team fights and sometimes crashes. =\
Well even at medium settings at 1080p you still won't be able to max out the game with a 5670.But the 5670 should get you to play on medium settings but i'm not sure about 60fps.Don't forget that the game depends on the CPU just as much as the GPU and that Athlon is aged quite a bit in the gaming world.