I decided to make this guide because there may be people out there who still need to use OS X 10.2 for legacy applications, or perhaps you just want it for nostalgia. Whatever the reason is you might want to run it in QEMU because PowerPC Macs are kinda expensive! You're gonna need a PC with QEMU installed, Windows, macOS, or Linux should work. I'm using Arch Linux for this guide.

Things you will need
1. OS X 10.2 iso
2. QEMU
3. A reasonably powerful CPU with a reasonable amount of RAM
(I'm using a Core i5 8400 and 12GB RAM)
4. Patience (this takes a while to get setup)

First make a virtual hard drive image using qemu-img or another tool to create them, tools like dd or fallocate should also work!
qemu-img create -f qcow2 ./102.qcow2 10G
This command creates a 10GB image named 102.qcow2 in the current directory.

Next it's time to start QEMU, here's the command I used:
qemu-system-ppc -L pc-bios -boot d -M mac99 -m 512 -hda 102.qcow2 -cdrom disk1.iso -netdev user,id=mynet0 -device sungem,netdev=mynet0
Replace 102.qcow2 with the name of your image file and disk1.iso with the name of your iso file.

If you made it this far you should see OS X 10.2 booting in QEMU! Now it's time to partition the drive using disk utility, pretty straight forward. Open Installer then Disk Utility and make a new partition! Next close disk utility and restart QEMU...yes that's right you want to restart QEMU otherwise it will fail the install. Once QEMU is restarted proceed with the install! I decided to go to customize and install the following:

Click install and it should start installing! If it says that it couldn't install it's because you didn't restart QEMU.

Once it finishes close QEMU, change your command to boot C and mount the second 10.2 iso, mine is disk2.iso!
qemu-system-ppc -L pc-bios -boot c -M mac99 -m 512 -hda 102.qcow2 -cdrom disk2.iso -netdev user,id=mynet0 -device sungem,netdev=mynet0

It will start booting and finish the installation!

Once it finishes you should see a welcome screen, set it up like normal! The registration isn't mandatory and can be skipped by pressing command + Q! (the windows key on a non apple keyboard)

Once you get to the desktop you can close QEMU and make some modifications to your command, I decided to increase the memory to 2048MB (2GB) as well as remove the cdrom portion, new command is:
qemu-system-ppc -L pc-bios -boot c -M mac99 -m 2048 -hda 102.qcow2 -netdev user,id=mynet0 -device sungem,netdev=mynet0
You can also echo it into a bash script which is what I did.

Now you have an OS X 10.2 setup running in QEMU, it actually doesn't run that bad on my hardware.

As you can see we have an internet connection and stuff, I haven't gotten audio to work nor have I tried. If I do find a way to get audio working I will update this guide. Anyways this system is good for testing old PowerPC software and stuff that doesn't require audio or 3D acceleration (both are broken).