Heres an example command definition that i use to use in my checkcommands.cfg file:
command_line /usr/local/nagios/libexec/check_nt -H $HOSTADDRESS$ -p 1248 -v FREEDISKSPACE -l $ARG1$ -w $ARG2$ -c $ARG3$
and the corresponding service check check_command definition:
This passes 'c' as ARG1, '10' as ARG2, and '1' as ARG3.
To find out what you can throw at your check_nt plugin, do this:
replace the path with wherever your check_nt plugin is. If you dont know where it is, try out this:
--wait for a bit--
$ locate check_nt
You should also look at your NSClient documentation to see what commands it accepts, what info it can return, etc.
Heres another example:
command_line /usr/local/nagios/libexec/check_nt -H $HOSTADDRESS$ -p 1248 -v CPULOAD -l $ARG1$
NSClient should be accepting the CPULOAD, FREEDISKSPACE, etc as built in parameters. This should be listed in the documentation for it.
This info might be a little bit off since i don't monitor windows boxes anymore, but you should get the idea from these examples.