Gateway P-6831FX laptop for gaming, [specs here]

Updated Vista to SP1, all updates current.

Searched the forums for an answer, but I didn't see anything that would solve the problem without regedit. Since I didn't use regedit to get myself into this mess, I hope I don't need to use it to get me out of it, since I'm not geek enough to mess with the Registry without adult supervision. Here's the problem:

I wanted to squeeze a little better gaming performance out of my laptop, so I followed one of those "Vista optimization" guides to turn off the Aero theme. I didn't notice any improvement, and in fact it seems to stutter even more while playing Call of Duty 4 on high settings. Now I can't get it back to normal, because I can't remember which guide I used, or which options I've turned off.

Appearance Settings no longer have the option of turning it on. I vaguely remember turning off some kind of service, maybe?

And, yeah, I know it was pretty dumb to do all of that without understanding how to un-do it, or at least keeping a link to the instructions.

Thanks.