I actually tested this to see what would happen. I have a G3 tower with only a CD drive, and I also have a G4notebook with DVD drive. I put the G3 tower into target disk mode (boot with the 'T' key held down), and I then attached the FireWire cable between the two computers, inserted the Tiger DVD, and ran the installer.
The computer rebooted and I installed 10.4 on to the startup drive for the G3. It actually worked ... and 10.4 tried to boot from the G3 hard drive. I shut down my G4 PowerBook and rebooted the G3.

