X11 for Mac OS X is an implementation of the X Window System that makes it possible to run X11-based applications in Mac OS X, for eg. Open Office or GIMP. If you are not using any of such applications in your Mac then it’s better to uninstall X11 from your Leopard installation so as to save up on the disk space. If ever you feel like installing it again then you can use your Leopard DVD to do so.
But the standard (move to trash) uninstall won’t work here, so we have to uninstall it completely using the terminal in OS X.
Write or copy & paste the following command in your terminal:
sudo rm -rf /Applications/Utilities/X11.app /private/etc/X11 /usr/X11R6 /usr/bin/open-x11 /usr/lib/X11 /Library/Receipts/X11User.pkg
That is one single line. Be very careful as a small typo can cause problems and you may have to reinstall OS X. Therefore do this at your own risk.