How can I easily tell if a PC is running 32 or 64 bit Vista?

To see if your computer is running 32-bit or 64-bit Windows, do the following:
Open System by clicking Start > Control Panel > System and Maintenance > System
Under System, you can view the system type.


(Source (http://windowshelp.microsoft.com/Windows/en-us/help/41531554-d5ef-4f2c-8fb9-149bdc5c8a701033.mspx))