I was going to play around with this prior to my 770 WSODing. I don't know how to do it under Windows, but with Linux you can setup X11 forwarding over VNC to get another device to work as another monitor over the network with lower bandwidth requirements than X11 by itself.

I've seen Windows shareware programs to let other Windows systems and Windows Mobile handhelds to act as second monitor over the network (or the USB connection on the WM handhelds). However, not run across anything for the Nokia ITs yet.