If you wish to download the Asterisk@home you can find the Download site at http://sourceforge.net/projects/asteriskathome/
The online Asterisk@home Handbook can be found at http://asteriskathome.sourceforge.net/handbook/index.html
A WORD OF WARNING
Make sure you change the default users passwords before putting your server on a public network.
I can guarantee that you will get hacked if you do not.
The default passwords are well publicised.
Specifically change the root, admin and maint user passwords from a ssh login to the server. Type help-aah to see the commands to use.