Viewport shader by Laurens Corijn - http://laurenscorijn.com

explaining.jpg shows some functions, but it's outdated and a lot of work to update. 
If you really don't know how to use it ask me on game-artist.net forums.

the normal version only works in Max 2008 and 2009 (due to shadow code). the noshadows version works in Max 8 and 9 also, possibly even in Maya.