You don't upgrade a video card, you replace it.
If you tell what connections for the videocard are on the motherboard (AGP, PCI, PCI Express 1, PCI Express 16) I'm sure somebody here can tell more about possible cards.
How about your PSU? Would it support a very high-end power consuming videocard? And - even more important - would YOU need such a card for what you are doing with the machine?
Just for looking at standard resolution DVD, or even a HD DVD, your current videocard probably is nice enough.
My home computer is a HP Pavillion a250n bought in 2003. While I know this may seem archaic by today's standards I've made upgrades elsewhere (RAM, updating the BIOs, etc.) and it still helps me get things done.
My question is can I upgrade the video card to support a HDMI or DVI connection?
I have a new monitor that affords me this option but my PC can only connect via a VGA connection.
If anyone knows what card(s) are available for my set up I'd like to know.