How do you cut hair in a 'halo' cut?   Is there a diagram on the
internet I can look at to understand this?  thanks!

Sorry, no diagrams, but I have found some videos for sale:

http://www.martinparsons.com/vs_halo.html  - you can download a
quicktime sample to see if it's what you want

Here's another video by Vidal Sassoon
http://secure.habia.org/Habia_Products_Videos___DVD_s_12.html

http://www.videoshelf.com/hair.htm