Yeah. I'd always go for PC100 or PC133 memory even if you're using 66MHz FSB only, just because they are the same price. Do you actually need more memory? Just don't go beyond 512MB or you'll have trouble. Usually abore 128MB you'll get greatly diminished returns.

was thinking on adding more memory since the sound blaster live! card can do soundfonts and requires a bit of memory to use.

The Big Race USA CD-ROM should have both the Windows and DOS installers, so you might also consider installing the DOS version just to see if it works given the fact that you are using Win98. Graphics memory requirements are much lower for the DOS version (1 MB vs. 8 MB for Windows version if memory serves).