My beige G3 (upgraded with G4/533, voodoo graphics, 120 Gb disc) refused point blank to boot from the Jaguar install disc if there was any other system available. I had to boot from an OS 9 installer CD and initialise the drive first, and then partion using the Disk Utility on the OS X install disc. It would not then install until I set the first partition to 7.5gb (not 8gb as the documentation states). I have not experimented to find the precise cutoff point. I trust this may be of help.