best way to combat spyware on windows computers?

[Sam3]

We use Spybot S&D, Malwarebytes, Super Anti-Spyware, but these tools are used mostly to clean out infected machines. We use Symantec Endpoint Protection as the enterprise-level anti-virus software, but still get infections. Lately the infections have been limited to one particularly nasty bugger; the FakeAV malware. For infected machines the best recourse has been to reformat and reinstall Windows and all drivers and applications.

Also, XP makes it almost impossible to run in a non-administrative mode. Quite a few of the applications that we run need to be run as administrator. Also, general management like installing printers or software is near impossible as a regular user.