my spec,
p4 3.6GHz (hyperthteading)
2x 160GB sata raid drives (raid 0)
1024MB ram
ATI radeon x800xt
soundblaster audigy 2 live 24 bit(has BIG driver issues )

even with this spec my frame rate drops alot when 2 full stack armies face off but then i have graphics ramped up to max.
with your graphs set to min or medium you should be ok, you dont need anti ailising when on the battle field, theres nothing to see.