I have a P4 1.8Ghz, with 768Mb memory and a Radeon 9600 XT card with 128Mb video memory.
I run it on XP professional, SP1.

Small battles with 4 units per side run beautifully, but with 12 units per side, all engaged in combat, it slows down considerably.

So how on earth do you get it to run smoothly on a P3 ?