Here are two (2) methods.
(1) - Burning a '.iso' file via 'Roxio Toast'.
Launch 'Toast'.
Click on 'Toast's toolbar's 'Copy' icon tab.
From the 'drawer' click on 'CD/DVD Copy'.
Drag the '.iso' file onto the panel beneath the toolbar.
Select which burner to use - via the small circular icon popup menu, to the left of the big red 'burn' button.
Click the (big 'red') 'burn' button.
(2) - Burning a '.iso' file via 'Terminal' ('/Applications/Utilities/' folder), enter ...
hdiutil burn
... press the space bar (to place a 'space' after 'burn'), then drag the '.iso' file onto the 'Terminal' window, and finally - press the <return> key.
'Terminal' will print out, line by line, the process of burning the '.iso' file.
Below are the 'Terminal' results of the above (second - 'hdiutil') procedure -
'Welcome to Darwin!
s:~ s$ hdiutil burn /Volumes/HD2/Documents/\*Downloads/ubuntu-6.06-desktop-powerpc.iso
Preparing data for burn
Opening session
Opening track
Writing track
..............................................................................
Closing track
..............................................................................
Closing session
..............................................................................
Finishing burn
Verifying burn...
Verifying
...............................................................................
Burn completed successfully
...............................................................................
hdiutil: burn: completed
s:~ s$ '
The above was performed via 'MacOS X 10.4.4'.
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The above two procedures were used to produce bootable 'Ubuntu' 'live' PowerPC CD's.
I intend (later) to perform the same steps (of either procedure - above) to produce a bootable (non-Mac) Intel (AMD) x86 copy, as well.