[How to determine whether a computer is running a 32-bit version or 64-bit version of the Windows operating system]

[for Windows XP]


If one does not work, try the other.


Method 1: View System Properties in Control Panel


   1. Click Start, and then click Run.
   2. Type sysdm.cpl, and then click OK.
   3. Click the General tab. The operating system is displayed as follows:
          * For a 64-bit version operating system: Windows XP Professional x64 Edition Version < Year> appears under System.
          * For a 32-bit version operating system: Windows XP Professional Version <Year> appears under System. 
      Note <Year> is a placeholder for a year.




Method 2: View System Information window


   1. Click Start, and then click Run.
   2. Type winmsd.exe, and then click OK.
   3. When System Summary is selected in the navigation pane, locate Processor under Item in the details pane. Note the value.
          * If the value that corresponds to Processor starts with x86, the computer is running a 32-bit version of Windows.
          * If the value that corresponds to Processor starts with ia64 or AMD64, the computer is running a 64-bit version of Windows.




Source : http://support.microsoft.com/kb/827218