RHEL5 Beta uses:
All of these are beyond Moodle's minimum needs. Numerous persons are also already using Moodle with PHP 5.1 (and the more recent 5.2) and newer database versions. I'm not sure how many people are using Apache 2.2 though. In my experience though, 2.2 doesn't break a whole lot like Apache 1.3->2.0 did so you should be fine. Best way to find out of course is to grab the RHEL5b2 release and install Moodle on it...