I play RTW on the following rig:
While RTW is an old game and won't use more than one core of memory it runs fine on my PC - I play at 2560x1600 resolution with everything maxed out. It runs smoothly.
I did use nHancer with my Nvidia card but they need to update the software as the latest version does not work with Nvidia drivers from 257.21 onwards.
If you've not used Vista or 7 before there are two simple rules before installing the game;
1) disable UAC
2) create your own program files folder and install the game there.
Also
3) keep the vanilla RTW in it's own folder - take a copy and install any mods onto the copy.