Panther: Mac OS X 10.3: Part III: "Updating Classic
With the Big Day upon us, I offer the following tip for people upgrading to 10.3 who still use Classic on an occasional basis. You can create a disk image (using Disk Copy) and install OS 9 and all support files there, including Classic apps if you so desire. This way, all your OS 9 material will be contained inside the image when you're not using it, yet fully accessible when the image is mounted. There are more instructions for how to do this on any of these pages:
I need only minimal Classic support, so I weeded the system folder down to the bare minimum by hand (why does the Apple Video extension still get installed these days?) For this I only needed a 300MB disk image, although others might choose 500MB just to be safe. I then put the image inside ~/Library/Classic Support (which is a folder I created just for this), but the image can reside anywhere. One neat trick with all this is that the disk image will mount automatically if you ever try to launch a Classic app. Another benefit with keeping the image size down is that you can burn it onto a CD for backup (although you'll need Toast if you want to make it bootable, as I did). And when you upgrade to 10.3, you only need to copy the disk image to your new installation and everything will still work fine... "