The PHP5 port by Kristof is already quite good, but not everything is working yet. But you can help by downloading/installing it and report any bugs found.
See also the roadmap:
http://ez.no/ezpublish/roadmap
You can find the current version of Kristof's work on pubsvn:
We cleaned up pubsvn a bit while moving it to another server. The svn repository of the unofficial PHP 5 port is now at http://pubsvn.ez.no/nextgen_php5 (for other related links take a look at the http://pubsvn.ez.no main page).