Well let me be honest with you.
$50 worth of update is almost impossible, i would advise you to get and 9700 pro (agp), you can get oe 256mg NEW for $60.
You also can get a 500w (maybe its too much) for $27.All on ebay, just to give you an idea.
This will make a dif you can see, and it will last you more as an upgrade.
hope it helped.
Tell us what you decided.
tc