VNC, or Virtual Network Computing, is software that makes it possible to view and interact with a computer from any other computer or device connected to the internet. VNC is even cross-platform, so a person using a Windows-based computer can connect to and interact with a Unix system without any problems whatsoever.
VNC essentially "converts" your computer into whichever computer you are connecting to. For example, if I am at home with my desktop computer running Windows XP and I need to use ArcGIS (or any other Linux program), all I have to do is run my VNC software and connect to one of CAE's Unix machines. Once that is done my personal computer will look and act like a Linux lab machine, and whenever I want to I can exit and use my Windows programs!
For those of you familiar with Windows' Remote Desktop, VNC does the same thing but allows you to connect to Linux machines. To realize the full benefits of VNC, you just have to try it yourself!