As somebody who had trouble getting Xcode installed on Sorbet with a Dual 2.0 GHZ G5, I can only hope you have a smoother experience than I did. I had to get vanilla Leopard tools, but I ran into so many issues getting an installer that wasn't corrupt, the installer to actually finish, and having to erase the incomplete installation directory whenever the install failed at the halfway point.
If I had to give any specific tip, I would say to use Pacifist to install just the CLI stuff individually from the install package. I don't remember which specific packages I selected, but this won't work if you really want everything from Xcode installed. Even with Pacifist, it was still an endeavor to install, but it was the only thing that worked for me. Then again, with your quad setup, you'll most likely have less of a problem (my CPU would spike and even almost max out during the installers).