usually tune-up software does more harm than good. Some are occasional recommended, like CCleaner. 7 does use more RAM and the remarks about it being faster generally apply to newer computers, but even on old ones it can do a pretty good job. I recommend looking at this: Optimize Windows 7
I don't know if I'd recommend everything it says, like turning off system restore (a bad idea on a 320GB HDD). What video card do you have? It may be the video card causing the problem with the games. 7 has more visual effects plus online games are pretty fancy these days, and an older video card might not be able to handle all of it.