Agreed. All related technologies have to scale in tandem. However, H.264 is a great first solution to the problem of storing and transmitting HD content.
Using QT Pro, export to DVCProHD and you should get completely smooth playback. It'll take up a lot of disk space but your G4 will have no trouble playing it. Use command-J to find out the framerate of the original video and make the export settings match it.
