"If card comes with expandable RAM"
video card with expandable ram? i haven't seen those since the trident pci era
what you can find is video cards using their own ram and taking ram from system, really annoying and wastes system resources making machine slow
in agp you can still find good video cards in agp 8x, mostly from nvidia, for the driver support
models like nvidia 6200 can be found, avoid nvidia 6200LE that uses ram from system, also 5200 can work, there is a 7950 agp but is hard to find and probably very expensive
on ati side you can find more new models, up to a 4650 with 1 gb of ram
http://www.amazon.com/Sapphire-Radoen-4650-DDR2-Graphics/dp/B002MLZPBY%3FSubscriptionId%3D16330PR1NAHTNCZP5602%26tag%3Dpriwat-20%26linkCode%3Dxm2%26camp%3D2025%26creative%3D165953%26creativeASIN%3DB002MLZPBYas always ati is not popular on linux for the driver support but user experiences are very different making results diverse
the video card you put will depends on the psu you have and if the cpu you have will give it good use
if you have a early P4 on that sis, don't waste your money and invest on a new pc with pci express
if it is a old amd athlon, older than a socket 754 it is a waste of money