Its probably a AGP system, Soo what you need is a good AGP card for about 200 dollars possibly less,
If you buy a budget 100 dollar card you will get budget performance and a slow motion game,
Also seems like you have a weak PSU , they probably put a 300w in there or soo,
Youll need min 400w ,, by good vendor like Antec or OCZ ,,,
gl,