Use the following steps on windows 7/Vista 64

   Click Start, click Run, type msinfo32 in the Open box, and then click OK.
   Expand Software Environment, and then click Running Tasks.
   View the values in the Min Working Set and the Max Working Set columns for each process to determine the process that uses a lot of physical memory.

Note The values in these columns are listed in bytes. The process that is not part of Windows OS and have lot memoery allocated as Max Working Set is culprit.