Yes its true.
PHP 5.1.5 does not have php5apache2_2.dll which is the library that is compatible with apache 2.2. In PHP 5.2 it will be inculded and so should work properly. You can however download that version from the php snapshots. The compatible lib wont be included in the stable version untill php 5.2. So you can run php 5.x with apache 2.2 but it is not guaranteed to be stable as you have to use a development version to make it work.
So in a production environment you would not want to run php 5.2 untill it is officially released(its still in development) so you will be limited to php 5.1.5 and so apache 2.0.x.
Edit:-
A php bug report with the same problem
http://bugs.php.net/bug.php?id=37436&edit=1