Well, if your model is the desktop model, then yes. if it's the small mini computer sytle. then you''ll have a hard time getting something to fit.. Maybe look at something like this. I know the best card you could get would probably be the AGP Sapphire 3850.. it can run Crysis, no other AGP card can as good as it. not sure if that matters, but it's probs one of the best cards thats not a PCI-E card.
Look here.
Newegg.com - AGP 4X/8X, Desktop Graphics / Video Cards, Video Cards & Video Devices, Computer Hardware