You should consider upgrading your Joomla to the latest v. 1.5.7, as multiple bugs and security issues has been fixed since 1.5.3
I believe there's been around 300 fixes to Joomla since 1.5.3.
You can download an upgrade patch here:
joomlacode.org/gf/download/frsrelease/83...Patch_Package.tar.gz
That said, I personally have seen some funny behaviour in Joomla on local servers, but I'll try to test CAMOS on PHP 5 as well to see if that will make a difference from the PHP 4.4.8 it's currently tested on.
Kind regards
Webmaster School
Daniel Duvald