Software.  The main software components you need for a working LiveJournal installation are as follows (the recommended version is noted):

Versions.  These are the recommended versions. The versions available in Debian Stable plus any security updates are commonly used for LiveJournal installations. It does not matter if you have a different, perhaps more recent, minor/incremental software version (e.g. 1.3.35). An exception to this point is mod_perl: version 1.99 is part of the mod_perl 2 series, which will not work with LiveJournal.

Hardware.  There are no specific hardware requirements for a LiveJournal installation, but Apache/mod_perl and MySQL can utilize a lot of memory very quickly. Determining the right amount of processor speed, storage space, and RAM depends on how busy your LiveJournal installation will be. A simple rule of thumb to remember is that posts and comments drive site traffic, not necessarily the presence of more users.