The easiest solution would be upgrade to Panther (10.3), which has an Apple supplied version of X11. As for 10.2, I think Apple released a version of X11, but I can't remember for sure. I don't use X11 myself, so I don't know too much about it.
To reset your root password, just boot from the OS X CD, and from the Installer menu choose "reset password". Also, I'd repair permissions (use Disk Utility) and don't use the root account at all. Use sudo before commands you want to run as root as long as you really know what's going on! Much safer.