Is there a way in OS X to change the desktop from Finder to something else (for example KDE from Fink)?
Basically, I want Finder to not boot up at startup, so no icons, no dock (but keep the menu bar)
I don't know if this still works; but in 10.6 you could define a different application to run in place of Finder. I did this for a iChat stand-alone "kiosk" once.
defaults write com.apple.loginwindow Finder /Applications/iChat.app
When you logout and login, the application you designated (in my case, iChat) will start. I suppose you could set this to XQuartz; but, again, I haven't tried it myself.
To back out the changes:
defaults delete com.apple.loginwindow Finder