I think your confusion arises from the fact you may easy assume that OS X is a more advanced upgrade to os 9
Unlike windows Vista, which has evolved from windows NT, os 9 was the last of the original macintosh operating systems that started with the macintosh in 1984.
When modernising such an old system became a major pain, Apple decided to ditch any further development after 9 and instead build a completely new os based on an entirely different base, namely Unix.
OS X has more in common with Linux than it does with OS9, they share no code, but Apple did put in an emulation layer so that os X could run old os 9 apps.
So in short, OS9 never had the application dock at the bottom of the screen, but the good news is that your emac G4 could at least run os 10.4 - Tiger.
You should upgrade the emac to 1 gig of Ram and buy a retail copy of tiger off ebay to modernise it (make sure the disks you buy are not grey coloured - but the full retail copies that will install on any mac)
You will not regret upgrading to oS X
or you may have os X on your mac!!
Press the option key on start up - you may get the option to boot into OS9 or OS X if installed