MemTest is a RAM reliability tester that runs under Windows. It evaluates the ability of your computer to store and retrieve data accurately. A correctly functioning computer should be able to do both these tasks with 100% accuracy day in and day out. A computer that fails these tests, perhaps because of old hardware, damaged hardware, or poorly configured hardware, will be less stable and crash more often. Even worse, it will become even less stable over time as corrupted data is written to your hard disk.

New in version 4.0: The MemTest Deluxe bootable CD now supports 32-bit and 64-bit CPUs.
New in version 3.8: The Pro version now supports command line control of how much RAM to test and when to stop testing, and can automatically spawn multiple copies of MemTest to maximize the amount of RAM tested.

Win95,98,ME, WinNT, Win2K, Win2K3, WinXP, VISTA, 7, etc.( 32Bit and 64Bit )
http://www.hcidesign.com/memtest/