Maybe upgrade to a middle class card. If your computer's motherboard and power supply can support it I'd suggest a Nvidia GT 240 or 250.
AND, if your case can fit the card. (It may not fit though)
Usually, if it doesn't work, your Video Card may not have the capability to run shaders.
However, a budget PC at this current time will run Shaders, but not at satisfactory frame rates.
But, after looking at a similar model computer, I doubt your power supply of 250 Watts will handle it. 400 would be the minimum.
So actually, you may be better off buying a newer, larger computer, and upgrade that also.
Just so you know, I'm not a very good source of advice...