To check whether my CPU was 32-bit or 64-bit, here's what I did (in Vista):
First open up the System Information tools from Accessories > System Tools
![](http://2.bp.blogspot.com/_xl08dEExoZk/Sw5u7-hCIMI/AAAAAAAAAtQ/7ADyAR1bM9U/s640/Untitled.png)
Then from the System Information, look for the System Type Row, and there you will have your answer:
![](http://1.bp.blogspot.com/_xl08dEExoZk/Sw5v6aLfRuI/AAAAAAAAAtY/Qoywj6f_0qU/s400/Untitled.png)
- x86-based PC: 32-Bit Computer
- x64-based PC: 64-Bit Computer