You mean that you would like to use your Digital Camera as a webcam, so to speak?
Correct me if I'm wrong here, people, but AFAIK the camera itself has to be webcam-capable, (it has to know how to send what it sees over the USB connection. I remember my moms Fuji camera being advertised as "webcam ready") and for all the digging I've done, the Nikon D100 is not webcam capable. Most professional cameras aren't.
For what it's worth, i HOPE I'm wrong, and you can use your camera how you want to. Good Luck, nonetheless.