Thanks for the reply. Unfortunately that did not work. From the Matrix, I can see that Apache 2.0 should be able to support PHP 5.3 too, so even without the PHP change something is odd.
I've actually tried this on a fresh XP VM too, with the same problem.
If I install both PHP 5.2 and Apache 2.0, then stop all services, switch the versions of both to 5.2/2.0, then restart all services, I get the same problem.