If you spend a little over 200$ then you can get this card which offers very good performance with most modern PC games: http://www.tigerdire...e...&CatId=1558
The thing here is that you will need a better PSU to support this card and ensure stability, you will also need a monitor that connects with a DVI cable or S-Video.
This one also offers almost equal performance, but you will still need a DVI monitor and a better PSU.http://www.tigerdire...e...&CatId=1558
Even though this card costs less, it has nearly if not equal performance of the others: http://www.tigerdire...e...&CatId=1558
Still would recommend a better PSU.
Right now, I am running a 300W minimum card on a 250W PSU, and the system is really stable.
For you, your computer will have a 300W PSU, and the cards are rated for 450W. They should work, but on high demanding games they might need more power. Right now, unless you want to upgrade your PSU, or buy a better computer, upgrading your card may not be worth it.