Malwarebytes and Superantispyware, do not support 64x bit XP as far as I have seen.
My apologies; you are quite right.
Unfortunately there aren't so many applications around for 64bit Windows.
SpywareTerminator
http://www.spywareterminator.com/legal/system-requirements.aspx works, but not in realtime, on 64bit systems. Or so they say. To my mind it is not in the same league, but is another antispyware scanner. I would highly recommend
not installing the toolbar nor the Clam AV component. (The toolbar comes with a module called WSG.)
If you are intermediate/advanced, and especially if you read Russian, AVZ antiviral toolkit is considered a powerful antimalware tool. Not for the faint hearted, though. I'd be very cautious about removing any item flagged as suspicious by this program.
http://z-oleg.com/secur/avz/download.phpSome elements of this will not work on 64bit Windows, notably the guard, and the boot-clean module. (If I read Russian I'd be able to explain this better.)
It is possible Spybot S&D may work, at least in part, on your system.
http://www.safer-networking.org/en/download/index.htmlI could not find any info on the system requirements section to indicate that it is limited to 32bit OS versions.
Hope that helps a bit. (No pun intended)