Thanks for the answer, but even changing the port to anothe number (in the "lampp" startscript and in the httpd.conf), the command "/opt/lampp/lampp lampp" gives me this message:
XAMPP: Starting Apache with SSL (and PHP4)...
XAMPP: Error 1! Couldn't start Apache!
XAMPP: Starting diagnose...
XAMPP: Sorry, I've no idea what's going wrong.
XAMPP: Please contact our forum http://community.apachefriends.org/f/
I am using another instance of apache (v1.3?) which serves a JSP/Jakarta web application (which have heavy dependencies/versioning requirements) which I need to run all the time, but I am planning to construct a website using a CMS which requires a more recent version of the PHP included in the old version.