with Tweak Vista

Aero effect is one of the amazing effect in windows vista , if you have desktop window manager clubbed with your windows vista edition you can enjoy the aero effect in vista.
What is DWM?
DWM (Desktop windows manager) previously known as Desktop Compositing Engine or DCE) is a compositing window manager, introduced with windows vista,that enables the windows areo
user interface. DWM requires graphic cards supporting directx9.0 and shader model 2.0.

Enable aero effect on unsupported Graphic cards in windows vista with Tweak Vista at Technix Update - Computer Tips and Tricks, Vista Tips, Hacking Tutorials, Firefox Tips

I hope this will help you to run aero with your unsupported graphic card in vista.