You'll probably need more than 512mb for those games if you want them to run smoothly. Obviously RAM is not the most crucial part since you already have 512mb. You may want to consider the GFX card if you got one that's almost pre-historic - higher end ones will give you more FPS and other bits and bobs.
I upgraded from 512 to 1gb a few months ago having been on 12 for a long time. Massive improvement in things for me, games particularly, especially loading times and high usage areas (loads of enemies on screen etc). Also in running a better performance is running a number of applications at once