Is there anywhere that I can download additional materials to add to the stock ones that come with the program. Also, I have a co-worker who somehow wiped out all of his materials. How can he get them back?
While I don't know of any on-line materials libraries available for download, it's really not hard to start building your own.
It helps to examine materials in the current library and study the parts involved, whether they're transarency maps, bump maps or reflection maps. Use Photoshop to open some of the default images. You can easily make modifications and create your own materials from there.
Also, it helps to create a library of textures from which to build new materials. I know Newtek has a nice collection intended for Lightwave users, but they're useful to just about anyone who does 3D modeling. You can find other free texture collections on the web as well.