Disabling Aero in Windows 7 is very simple:

Right click the Desktop
Click Personalize
Under ‘Basic and High Contrast Themes, click ‘Windows 7 Basic’

Source: http://www.pcmag.com/slideshow_viewer/0,3253,l=251692&a=251692&po=12,00.asp

Source: http://www.thewindowsclub.com/does-disabling-aero-really-improve-performance-in-windows-7