If you want to install Apple Tiger or Leo on an Apple Intel, the hard drive must be formatted first "GUID." If you have any other format, you must first zero the drive because the Apple format utility can't reformat into GUID unless you do. Then you cross your fingers and hope it works. GUID uses the last sectors of the hard drive for the MBR, which violates some drive maker's bios rules.The illegal MBR of GUID allows dual booting Windows by prevent Windows from tampering with the Apple MBR.