installing multiple mac OS's on a powerbook

27 houdini's

guy with great hairdo
for testing purposes i would like to install multiple os's on my computer:
OS 8.5
OS 9

next to my OS X. Is this possible? Do have to make different partitions on my drive (which i would like to avoid)

I understand that the classic environment in OS X 10.3.9 is limited compared to the original OS 9.

powerbook 15ii G4 1 mb ram OS 10.3.9
I didn't get what powerbook you are actually using. This is important to know since most of the recent powerbooks don't allow you to boot into <macosx. I think my 15'' tibook was one of the last that supports os9 (anno 2003). Anyway, if your powerbook does allow you to boot into os9 you won't need to setup different partitions. Jaguar was running on the same partition as os9 when I got my tibook.
Not sure about os8.5..
i got a 2003 model, with classic as an option though not installed.
but i wonder if i can install the OS's just like a regular app, like photoshop for instance.

I am not shure but i think you are not right about later model not supporting classic (or OS 9)

Machine Model: PowerBook G4 15"
CPU Type: PowerPC G4 (1.1)
Number Of CPUs: 1
CPU Speed: 1 GHz
L2 Cache (per CPU): 512 KB
Memory: 1 GB
Bus Speed: 167 MHz
Boot ROM Version: 4.7.1f1
You can simply install the OS just like a regular app. Once you want to boot into that one (aside the Classic mode), you simply open Startup Disk in the System Preferences and let it scan for bootable systems on your disk.
Newer Macs (let's safely say after 2004) are not booting into OS9 anymore. Search the forum for threads on this topic.
Your powerbook is a titanium book such as mine. It should boot OS9.
you're writing suggests that booting into os9 is hardware related. why should it be?

nice cat by the way
It's not the hardware that is preventing OS9 to boot but the software. I am not sure how this blocking works but I believe it's firmware based, since I heard about some firmware hacks to open this lock. However, you might be asking yourself why Apple does so. I don't know but it makes a bit of sense to me: new hardware needs certain adjustments in the software. There is no more tech and driver support for older OS so the harmony between older software (OS) and newer hardware must be disturbed somehow. To prevent the user ending up in some indefinable problems, Apple decided to block the boot of such older systems. But as I said, I actually don't know. If you are interested I suggest you to read our old threads on this.
Thanks for the comment on my cat. He is a lot older now and looks a bit more "round". ;)