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You could also burn your own OS X disks based on those disk image (iso) files. Note that this will be the only legal way to obtain an installation disk. Purchase a retail disk of OS X 10.4 Tiger (or Panther) and include that, when you're selling your iMac. You can open and mount an individual disk image (.iso) and fool the installer, so that you're computer believes you've inserted an installation CD-ROM, yet you will not be able to boot from a disk image file afterwards. The OS X disk you're using will not work as is.
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you can, it isn't necessarily straight forward though.) Nor can you merge two partitions without erasing your drive. It would be like going climbing and cutting your own rope. As Barbara has pointed out, you can not erase you're startup disk without booting from a different volume.
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