You can use Disk Copy under OS X 10.1 to make a .DMG file, which is essentially the same as an .IMG file. If you want an .IMG file, I think you'll have to use OS 9's Disk Copy to do that.
Open Disk Copy, and select "New Blank Image" from the "Image" menu in the menubar. Select an appropriate size, like 650MB for a CD or however large you need it. After you hit OK, the image should mount, and you should have two files on your desktop (er, one file and one volume, which is the mounted image file -- like a disk). Drag 'n drop your files onto the "mounted volume" and it should copy them over. Un-mount the volume you made by highlighting it and hitting Command-E (under OS X) or Command-Y (under OS 9) or simply drag it to the trash. It will unmount. You will now be left with either a .DMG file (OS X) or an .IMG file (OS 9) that contains your files.
To check it, double-click the .DMG or .IMG file and it should "mount" again, intact, with the files you copied over there.
Good luck!