even if you upgrade your your psu I would not go much higher than a 5770 and even that would likely be pushing it, otherwise Id be looking to the used market and ebay for a gts 250, gtx 260, 4850/4870 or something similar.... if you want more performance than that (although will already be seriously held back by your current cpu) your def due for an upgrade keep the current machine as an htpc or something and build a new one
Like others have said, i dont know what you plan to do with this pc, gaming? general office use? media playback? If its just general use or media playback, just get a low end card like 5570 or gt200, these cards can play older games but forget anything new. But agreed that with your current power supply you are very limited and even low end cards like the ones i have mentioned may tip the psu over the edge. Replace the power supply with something like this http://www.newegg.com/Product/Product.aspx?Item=N82E168... which is a great deal if you have access to newegg. you can then run a 5770, gts450 or even a gtx460 and not be scared that your psu will explode. it also leaves room for upgrading other components like your cpu, motherboard etc in future. With your current cpu i would not go more than a 5670 or gt240 or you will suffer a cpu bottleneck, where getting a more powerful gfx card wont benefit you as the cpu is the limiting factor.
i use this computer just for kick-back. nothing serious really. its been years since ive gotten it and it was on the crappy side so i thought maybe i could fix it up a bit but i guess i should just get a new one. thanks for the help guys it really helped