windows 98 can be your potential problem. Should upgrade at least to 2000. Xp pro would be FABULOUS! IF you think that isn't the problem, give EA a buzz. They should come up with the right solution.
i run windows 98 on a AMD athlon 2000+, 256 DDR RAM & I have the same video card as you GeForce2 MX-400 & I have very little choppiness...maybe a little @ the start of the game as all the graphics are loading in but after that...pretty sweeet 8) .
Its is one of your USB devices, more than likely your mouse. Or you may have a NON USB device using a USB adapter. Read my threads and you'll find your answer without purchasing anything.