I got a G3 iMac which has OS X Tiger 10.4.11. Can i install OS 9.X and run it in classic mode without having to partition or format the hard drive?
The iMac has the original CDs that came with it with OS 9.0.6 (i think).
The specs are:
iMac G3 (Slot Loading) 450Mhz
388Mb Ram, 7GB Hard drive
OS X Tiger 10.4.11
Yes. If you only want to use classic mode under 10.4, then simply put in the CD and install OS9. It will be installed on the same partition as your 10.4 Tiger installation. Easily done.
Your iMac should be able to handle OS9 natively too though. Might give you higher compatibility, especially for older games. (and a much better performance) Though you will have to reboot every time you want to use it. Unless you stick with OS 9 like I did 
If you want to boot with os 9 natively, restart, hold down the option key and choose OS 9.
Whilst your machine will run OS X 10.4, it will be slow with a G3 processor, 384MB RAM and
8MB VRAM. Like Bolkonski said, the iMac will perform with OS 9 way better.
Ironically you could buy a 2nd hand fast G4 eMac for about the same money as you would get for your G3. People see them as old, slow and heavy computers - which they are compared to any new Mac. All you need to do is be lucky and find a local seller.
You can try the following:
Download http://support.apple.com/kb/DL1192?viewlocale=en_US . After mounting the .dmg you find English/NetBoot.pkg and and in this .pkg (with ShowContent or ShowPackage or ...) you find NetBoot.pax.gz, copy this file to your hard disk. Then double click it. A folder "NetBootInstallation" will appear with size 0. But if you change the rights of this folder to read/write you'll find "NetBoot HD.img" with a 9.2.2-System in it. Open it and copy "Applications (Mac OS 9)" and "System Folder" to your hard disk.
If you take the NetBoot image approach, you also have to delete the Multi User Preferences file when you copy over the System Folder. Otherwise you'll be asked to log in to OS 9.
