API for seeing if my program is running in a VM environment.

Hi all:

I am new to the forum.

I have several software packages I have wriiten and am concerned about one license being purchased and then loaded onto a server and running in a virutal environment like Citix.  Is there a way I can have my program detect that it is being used by several individuals for a single server?   Are there APIs that identy the thin clients ID or MAC address. It seems most of the normal Windows APIs just return the server's name and MAC address.

Thanks