timing accuracy in Windows

Hello,
I am interested in the timing accuracy and timing resolution in the
Windows version of Psychophysics Toolbox. I looked around the web
site briefly, but did not see any timing tests/results. Also, I was
wondering how you enforce the timing? Is it through some Matlab
functionality, or did you have to use specific Windows function calls
to do it? Any information would be greatly appreciated.
Thanks,
Trina