OS 9 drivers can be installed while a Mac is locally booted from OS 9 (another HDD or a CD), booted from a disk image, netbooted, in FW target disk mode from another Mac, or while the Mac is locally booted from OS X. In all cases, it involves reformatting the target drive to install the OS 9 drivers and provide all the partitions of the Apple scheme, only the fourth of which (out of at least five if you have only one desktop-mountable 'volume') contains the mountable volume, and the SCSI driver lives in the second. Have a squizzy in this fred.

If you wish to install only OS 9, you have no choice but to boot, format and install from OS 9 by any of the above means. If you wish to install OS X also, you can boot and format from OS X, but the formatting process must include the option to install OS 9 drivers if you wish to continue to be able to boot into OS 9.

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