How to determine if your Windows version is 32-bit or 62-bit?

(Windows XP)
Click Start button. Right click My Computer > Properties.
Under System tab, if you see "x64 Edition", your Windows XP version is 64-bit.
Otherwise, you are running 32-bit version.

(Windows 7 or Vista)
Click Start button. Right click My Computer > Properties.
Under System tab, the system type is listed.