You need to find the (program files)\Autodesk\3dsmax 2008\mentalray\shaders_standard\include\production_max.mi file and open it in a text editor like, say, Notepad
Then go through this file, and find every instance except the first one of a line that reads:
"hidden"Change this line to instead read:
(I.e. add a hash mark in front).
Restart 3ds Max 2008... and the shaders will be available!
NOTE: Do not remove the first instance of "hidden" because that is only for a dummy placeholder phenomena which exists only to contain the gui definitions themselves, and the dummy is not useful for anything at all, so leave that as "hidden", or it will just clutter your UI with somethign that looks like a shader but isn't.....