It does not get any EASIER than this disk.
Download it ( asteriskathome.sourceforge.net/ ) and burn the ISO image to a CD.
Boot a computer with it (but make sure its a computer that you are going to basically dedicate to Asterisk because this install will overwrite everything on the computer).
Once booted, youll be shown an installation screen. Press enter, and let it do its thing. It will take about an hour on a computer…but once its done, the OS and the entire asterisk solution with all the bells and wistles is installed and ready to go.