Currently Being ModeratedJan 22, 2013 10:32 PM (in response to yini1)
You need to use a retail DVD and not the iMac's original disk to upgrade.
Currently Being ModeratedJan 25, 2013 5:21 AM (in response to yini1)
Niel is correct. Only the retail 10.6 installer will install 10.6 on a Mac Pro that currently is running 10.4.4 or later. You can't be running 10.4.1 on a Mac Pro. You sure you have a Mac Pro, and not a PowerMac G5? Or are you just dropping the zero on the end of 10.4.10 in your signature? That zero is significant if it is there. No Mac that runs 10.4.1 can run 10.6. But about half the Macs that can run 10.4.10 can run 10.6, but they must have a built-in Intel CPU.
explains other pitfalls you may run into when upgrading to 10.6.