Moodle 2 may well use the new PHP 5 features and require PHP 5, but this is a long way off. I personally haven't even installed PHP 5 anywhere yet.
Moodle 1.x will continue to work fine PHP 4.1 and later. It will probably work fine under PHP 5 but it's not well tested yet. For a Moodle production server I would stick to PHP 4 for the time being.
General developer forum
PHP 5.0
This discussion has been locked so you can no longer reply to it.