Simply copy Shoestring_shaders.dta and Shoestring_shaders.mcx to Eovia\Carrara Studio {2.0 or 3.0}\Extensions, or to any subdirectory under it. I like to keep my plugins in separate directories to make them easier to locate. So I have a DCG directory, and a Shoestring directory, for instance.
Same as above, but the path is \Carrara\Ext.
When you initially use one of the shaders, ie add it to a shader tree, a dialog box will open and ask for your password. To evaluate the software, just hit cancel, or ok. You can even guess at a password if you want. In evaluation mode, a random portion of the object you are shading will be black. Every time you open a file that includes a Shoestring shader, or add one, you will see the dialog. Once you have purchased the plugin, a password will be emailed to you- simply enter it in the box, and two things will happen. The black spots will go away, and the box will stop popping up.
www.desweb.net/shoestring_graphics.html