First let’s see what exactly these numbers 32 and 64 represent. These numbers 32-bit and 64-bit represent the Data Bus width that are between the Memory (RAM) and the Processor. Obviously you can see that 64-bit has the capability of carrying data twice the width of 32-bit.
now here is simple way to check processor is 64 bit or 32bit,
The following works for Windows Vista and Windows 7:
You can find out by going to Control Panel -> System and Maintenance (System and Security for Windows 7 users) -> System.
Alternatively you can search for System on Start Search,
For Windows XP:
If you’re running Home Edition, you’re using 32-bit. Professional shipped as 32-bit and 64-bit, but almost nobody uses x64. To check go to Start -> Right-click on My Computer -> Select Properties from the Menu, from there the 64-bit versions will be listed as Microsoft Windows XP Professional x64 Edition. Otherwise you’re running 32-bit.