The current version of the library can be downloaded here. The file 'matlib.blend' is just a repositry for materials, so if you open it up all you will find are a load of planes that act as place holders. Here is a brief 'how to' that should allow you to create an object and then 'paint' it with the material of your choice from the library.

(1) Open up a fresh Blender project ('ctrl+x') and add a new UV sphere. Add a couple of lights and a camera so that you have a nice test scene.

(2) If you render an image now, the new sphere has the horrible default Blender material - not very pretty.

(3) Now hit 'Shift + F1' to call up the 'Load Library' menu. Hunt around your hard-drive until you find the matlib.blend you downloaded and select the file. Now you'll see a menu of all the different types of objects that Blender uses, with 'Material' about half way down. Select 'Material'

(4) Now you'll see a list of all the materials contained within the matlib.blend file. Hopefully the names are fairly self explanatory, but if you want a visual reference, the 'Thumbs' page from this site is included in the download.

(5) Choose 'Marble1' from the 'stone' selection with a right click. It must be a right click rather than a left, and the material you have chosen should become highlited in blue. We only want one material, but if you needed more its just a case of 'right clicking' until you've highlighted everything that you want. Then hit 'Enter'.

(6) Back in your test scene, select your sphere and go to the Materials menu with 'F5'. Now if you hit the little minus key, the material that you chose should be sitting there in the drop-down menu. Select it and it wil be applied to your sphere. Now render away...