Consider getting a new one - and not an OEM (major manufacturer/prebuilt) but either assembling it yourself, or have a shop do it from a parts list supplied here.
Really, to do the job right, you pretty much will need to replace everything. If that's an option, I can supply a parts list based on what you can afford. Apart from that, do what I mentioned in my post: Get a GT430 and, if you see you have some memory slots free, buy enough memory to bring you up to 3 or 4Gb. You can probably do that for about $100, maybe quite a bit less if you can get the video card on rebate at Tigerdirect.com. A CPU upgrade would help too, but the CPUs that will work with your board are long out of production and a decent upgrade is about $200 for the CPU alone. All told, you can build a better machine for less.