Just buy an x1900xt which are relatively cheap. That'll help no end. As it is you won't be playing many games on that pc unless you're fond of pacman or something.
And whilst I haven't played MTW2 it is an evolution of Rome TW which is pretty much the same as shogun but with fancy additions. You don't get cool samurai tho
EDIT: You could buy MTW 1 which will run on you machine come to think of it. That's very similar to shogun but obviously set in Europe and the scale is much bigger map wise.