When you say "G4 eMac" you are hopefully referring to one of the first two eMacs that originally were capable of booting OS9 natively.
If not, you're probably SOL. Booting OS9 on unsupported eMacs is still wishful thinking
See here:http://macos9lives.com/smforum/index.php/topic,2466.0.html
If so, fine. Keep reading.
If you want to keep Tiger and have a dual-boot machine, you'll have to start by re-formatting the entire drive. You can do this in OSX (I'm assuming you have the Tiger Cds or DVD).
From the Tiger install disc:
1. Initialize the HDD with "OS9 drivers" checked
2. Partition the HDD in two. (What sizes I can't say - I don't have any idea what you'll be using. If it's big enough, cut it in half)
3. Install tiger into one partition.
Note: Installing OS9 Classic is optional. You CAN have both OS9 classic and a full OS9 on the same machine. While Classic basically sucks for anything audio, it can be useful for other small things in a dual-boot setup. If you're unsure, leave it out - you can add it later if you want.4. Go to >>System Preferences / Spotlight / Privacy<< and prevent spotlight from searching the other entire soon-to-be OS9 partition.
This is important - Spotlight will repeatedly frack up your OS9 files otherwise!Then: Download the Universal 9.2.2 image from here:
http://macos9lives.com/smforum/index.php/topic,305.0.htmlFollow the directions to use Disk Utility to install OS 9.2.2 into its partition.
Enjoy.