An alternate method [?] My G4 GE (used) came w/a 20Gig drive & 10.3.9. I wanted a large drive & Tiger. A. I simply 'added' a 120Gig drive, cloned the old disc contents (keeping all the apps and 10.3X on the 'new' drive). B. I then rebooted to the 'new drive' & installed 10.4 on the new drive. So, the new drive (120Gig) had 10.4 and the old small drive had 10.3X PLUS all the apps. I stayed 'in' the new drive and continued to add apps to the new (10.4) disc. (I've since done the same 'switch' on the small drive...keeping the original 10.3 on Drive '1', my 2nd drive) Anyway, even with the older OS & many apps on the 'non-boot' drive I can execute any app installed prior to the 'clone(s)'. Though I need not access the old OS, I thought it worth mentioning that it was NOT necessary to re-install any of the many apps on the 'original' drive. I will install 10.4 on the 2nd drive as well, but for now I am able to boot to either drive and and have an OS. The point? Since an OS occupies little space (and drives are cheap & the G4 has 'size limits per drive') I've found it best to have and OS on 2 drives as even each can operate as the 'boot' & all apps function. Should there be a problem with one drive it's possible to boot to the alternate drive & often any 'fix' is easier with a full set of tools (on each drive) to attack an problem on the other drive. FYI, I've fond SuperDuper does a fine (not fast) job of 'cloning' one disc to another.