Raub: Leadtek Ti200 is built on the same mem and architecture like their gf3 TDH, 3.8ns ram, same cooling, same 2D filters (getting one of those..)
Added bonus is that the TDH is famous for its 2d quality.
Top: when you look at your framerates, make sure you have your framerate limiter set to unlimited in videomenu. If it's set to 45 or 60, even geforce3 won't give you more than 50 fps maximum.
Also check your monitor refresh rate in-game. If it's 60hz, use the nvreffix proggie to fix that.
BTW: I hope you're using W2k or XP since W98 / ME core is not able to handle memory above 256Mb so you're wasting your money buying ram in those OS's. Adding too much RAM has also often lead to stability problems with Windows98. It gets confused trying to allocate the memory I think.
With 700+ Mb RAM you _must_ upgrade to W2k or XP if you want any benefit.