get everest (www.lavalys.com
) and then use it to see what kind of a vid card u have.
And yes u can upgrade just the vid card.
There are 2 things that u need to make sure when getting a new vid card.
1. Make sure that ur mobo has the interface that the card uses (pci, agp or pci-e)
2. Make sure ur psu has enough juice to run the new card.