Time to show how sad I really am....!
Combat FS eats up power and resources like nothing else around. Unless you have a P3-500 or similar and one of the latest 3d accelarators, you will have to turn down the graphics detail to get an acceptable frame rate. Once you destroy that pesky Hun, hundreds of little polygons are created as he falls to bits and your system obviously can't cope.
I doubt it's a memory problem, but you should definitely have more than 56% of system memory left after bootup. You probably have loads and loads of useless little programs starting up and running in the background - get rid.
Swapping to a decent 3d card (Voodoo 3/Matrox et. al.) would help immensely.
I also found that win95 runs somewhat faster than win98 and have reverted to that.
Cheers