Manually Installing X11
If you want to install the XFree86 distribution manually, download the distribution (see the instructions on the XFree86 web site) and run the Xinstall.sh script to install the XFree86 suite.
This script will prompt you for some configuration details, although it includes defaults that should work for most Mac OS X users. The XFree86 web site has an extensive set of instructions explaining how to install XFree86 for the first time, how to install the suite over an older XFree86 installation, and how to uninstall XFree86. There are specific instructions for Mac OS X and Darwin.
The installer script will install the X11 binaries, libraries, header files, manpages, configuration files, etc., in /usr/X11R6 and /etc/X11 .
There is very little difference between manually installing XFree86 on Mac OS X and manually installing it on other Unix systems. The main difference is that some files required on other Unix systems are not required on Darwin. For example, there is no separate Xvar.tgz file to download. Another difference with Mac OS X is that the double-clickable XDarwin application is placed in the /Applications folder.