Thanks for your reply, Tellos, and all the others who replied.

I'd say you should look for a card with a healthy dosage of onboard RAM
That's why I asked about the 512MB graphics card, although AGP. I know AGP is yesterday, but I do not want to do major changes, since my computer is running very well with most games (I even got FSX to run smoothly) and I don't want to spend so much money. Going for another type of card than AGP would mean I would have to change the mainboard, and then I could change the processor as well, and then the RAM.