I've noticed quite a few Open Source programs aren't very compatible with PHP 5.3 and some aren't compatible at all.
The good news is you CAN still download older versions of XAMPP until Joomla or whatever other programs aren't quite yet compatible with PHP 5.3 get updated.
PHP 5.3 had quite a few major changes to it, so there's going to be a lot of PHP apps that will need to be majorly modified.
Anywho, XAMPP 1.7.1 works fine with Joomla 1.5 and has PHP verison 5.2.8.
You can download it from:http://sourceforge.net/projects/xampp/files/XAMPP%20Windows/1.7.1/xampp-win32-1.7.1-installer.exe/download
As a future reference, every version of XAMPP from way back can still be found on SourceForge.net.
Here's where you can find those:http://sourceforge.net/projects/xampp/files/
They are listed in descending order, meaning the oldest versions are on top and the latest versions are on bottom.
Hope that helps!