It cannot be done, since switching OS requires unloading and reloading of all the system files. The machine's state must be initialised to that of when it was first started to be able to load another OS without problem. I'm not familiar with Macs, but from what I've heard most of their OS is in the firmware. That is probably what makes it possible for their architecture. With overburning, nearly 900MB of storage space can be possible on a good quality of CD-R. Also, optimisation at the file level allows such things as 10-in-1 CDs.Just use magiciso to make iso image with checking the option "The same files are only allocated once". http://www.magiciso.com/