You will find that the ETW game engine is a lot newer than the RTW one and does take advantage of more modern machines. Although when first released ETW didn't take advantage of multiple cores or even decent graphics cards (I had a two GTX280s in SLI and the game had error messages about not enough video memory).
Anyway, the things that you can do to try and improve performance is have a look at the services that are running on your system and use msconfig to stop the unwanted services. You could always use IOBIT's Game Booster software to put your machine into 'gaming mode' :
http://www.iobit.com/gamebooster.html
Hey, at least you aren't trying to play Shogun or Medieval Total War with a Nvidia card - both take exception to anything other than dated cards (8 series onwards).