Yes you can still pickup 64 or 128 MEG PCI Video Cards which will work on that system. If you are looking at new Video Cards I don;t think that you'll see any under 128 or maybe 256 MEG but this depends on where you are buying and how old their stock is.
If your processor and installed RAM is more than the minimum system requirements of the game this will work. Also with a 100 MHZ FSB you could conceivable go to a 800 MHZ P3 CPU or the equivalent in the AMD camp. Depending on the M'Board involved but things like the old BX440 Chip Sets will support a 600 MHZ CPU with ease and at a pinch a 800 MHZ will work. As I've always been running Dual CPU M'Boards the 600 is the biggest that will be accepted on these Chip Sets but if you are only running 1 CPU you can place an 800 or 850 MHZ with a 100 MHZ FSB onto the Board without a problem. There where even some 1 GIG CPU's that had a 100 MHZ speed though these are rare and hard to find.
Col