Want to still use Aero, but lighten up the features a little? One of the heavier aspects of Aero is the transparency (as it was with XP), so turning it off can save you a little resources.
* Right click on the desktop and select 'Personalize'
* Select 'Windows Color and Appearance'
* Uncheck 'Enable Transparency'
You still get all the other benefits of Aero, but your system should be a little less sluggish.