I believe that minimal number of threads is one. Why not checking it up?
I would suggest using Sysinternals Suite (Sysinternals is not a part of Microsoft):
http://technet.microsoft.com/en-us/sysinternals/bb842062[
^].
These are two utilities you can use:
http://technet.microsoft.com/en-us/sysinternals/bb896653[
^],
http://technet.microsoft.com/en-us/sysinternals/bb896645[
^].
The results can be sometimes interesting. For example, the process using at least one file dialog adds a thread for dialog activity (I hope you can understand why).
I would say, Sysinternals Suite is must-have for all software developers, to complement other Microsoft development tools.
—SA