Video card upgrade for Dell XPS laptop?

I have a dell XPS laptop, with a Radeon 9700 Mobility 128MB AGP (I'm pretty sure its AGP) video card and want to upgrade to a 512MB card. Will any AGP 8x video card work or do I need a more specific card? If anyone can provide a site or links to a list of usable cards, that would be much appreciated too. THanks!!