use CCC or another cloning app to at least 2 external firewire HD's

HD's (with FW4000) of 250 GB are cheap and easy to test from time to time

don't clone to a serie of DVDs, self written dvd are not secure/save enough, if one DVD isn't readable after some time, it's possible you don't have a usable backup/clone at all

the best way to perform a clone is by connecting the indigo imac and another mac with a firewire 400 cable

start up the indigo imac in target disk mode (starting up with key T pressed down)

and the other computer as usual

the HD of the indigo imac is shown as firewire symbol on the desktop of the other mac

clone the HD with CCC, on the working mac