Hi hustnn,
When you build a private network it depends on what you want to archieve.
The easiest way is to build an unencrypted network among friends. For that you can simply use Phex and set a private network name. Only people who set that name can join you. Your friends then set the same network name and enter your IP to get connected. Afterwards the Phex' exchange the addresses themselves, so that your IP is only necessary on the first connect (or when every known member of the network changed the IP while the user was offline).
An encrypted private network is a bit more complex. I'd use i2phex for that:
forum.i2p ~ View Forum - I2Phex
You can either just use the normal network (exchange with every i2phex user, but anonymously) or also set a private network there - with the advantage that the address people need for their first connection can be anonymous, too.
The installation of i2phex requires first installing i2p and then i2phex - ideally compiled from source. If you use a GNU/Linux system, the source download and compilation step is only
Code:
svn co https://phex.svn.sourceforge.net/svnroot/phex/phex/branches/i2phex i2phex
cd i2phex
./build-and-run
Happy sharing!
@LotR: Thanks for editing swiftly!
PS: Infos on compiling i2phex yourself:
http://forum.i2p2.de/viewtopic.php?t=2357