That is really old one that I think come back from 2003, So there is probably small difference on your graphics when you upgrade to this. By the way I found 'fast' PCI GPU here at newegg: http://www.newegg.com/Product/Product.aspx?Item=N82E16814161353
It's 5450, I think it's pretty slow and it's comparable to ~HD 2000 Graphics. But much better than the card you showed me.
And still I think it's not worth it to get only PCI card's, because for the same price you can get a 6670 that's much faster. So I think it is bestfor you to upgrade your whole system.
If you worry with newegg, don't worry. Newegg is probably the most common store in this forum.