I hope someone can help me. [I just upgraded my 10 year old (!) G4 to a new iMac.] I have an external hard disk with a system folder 10.4.x (whatever the very newest update was.) I was planning on using that system with my new iMac (with 10.5.7). When I going to System Preferences>Start Up Disk.... it doesn't recognize the system folder in anyway. Is there something wrong or can I simply not do this from my new iMac??? Thank you much.