Monitoring windows can be a real pain. I plan on writing a nice HOWTO on this subject RSN.
For now let me state your options (keywords you can enter into Google for example):
NRPEnt is a daemon that works with the check_nrpe script and configures kind of like the normal NRPE daemon. NSClient uses all kinds of WinNT internal counters.
NSClient++ is a combination of NRPEnt+NSClient.
Using SNMP is the most versatile, but also -very- difficult for the beginner.