Do not use Aero 3D in Vista if you use an integrated graphics card with 1G memory.
Integrated graphics card uses dynamic memory technology, allowing it to borrow system memory for its own use.
However, as the number of running applications grow the need for graphics memory also grow considerably. In this case 1G memory is devided to meet the heavy needs of both applications and 3D graphics. The result? Hell.
So just turn Aero off.
Also, if your laptop is on a battery, Aero 3D will eat up approx. 20% of your battery time.
Here is a tool to turn Aero off automatically once you are on battery.