As of mpentoo 2006.1, you don’t need this. Simply type pinstaller at the cmdline or launch it from the menu in Misc. the following is just for 2005.1 backward compatibility
Here is a document and a script that will teach you how to install Pentoo 2005.1 on your harddisk.
Unfortunately, you’ll need to read the doc to install it as this is not done as is by running the script...