I have received many e-mails of people complaining that vista is running is slow on their systems. Most of them complained that when they turn on aero effect, the computer gets very slow. I asked them the configuration of their systems, most of them have :-

• Intel Pentium 4
• 512 MB RAM
• 40 or 60 GB hard disk space
• Video Graphics card
• Other normal configurations

Some reasons:
1.) Maybe, a bit larger RAM is required to run Vista smoothly on your systems! Microsoft did not leak out the correct minimum configuration to run vista, in order to get more costumers. Actually if they must have given that it requires more RAM, the customers may drop the idea of buying vista due to their low budget.

2.) Some technical error of files may occur.

What to do?
1.) Ask for technical support from Microsoft.
2.) Try increasing your RAM by buying a new one.
3.) Increase your virtual RAM.

Links :- Microsoft Support