I have a Mac G4 that I brought back to life and it’s funny how people run into the exact same problem. When I installed OSX I forgot to add X11 and I dont have DVDs/CDs for it. So I googled it up and found this: http://cjmart.in/2006/12/01/install-x11-on-tiger-without-the-tiger-install-dvd/
The dmg
http://idt.lcc.gatech.edu/~cmartin9/files/X11Tiger.zip
Funny enough the reason he needed was for NX which I ran into ;)
Kudos to Chris Martin