G4 ! Who cares about your crummy old G4! This is a fantastic program. Just kidding. Heh. Of course they should make sure it works for all the old macs out there including your G4 and my old Macintosh IIci. But hey, it is a great program. Works perfectly on my G5 PPC dual running latest 10.5.8 Like a friggin super-charged planetarium sitting right on my desk. So 5 stars to balance out the score. If you're interested in the night sky and you haven't tried this yet, don't wait. It's really great. :-)