Here is how you turn a dmg into an iso on OS X:
- Open a terminal.
- cd into the directory where the dmg is located
- Type this in where newfile is the name of the iso you want, and yourfilename.dmg is the dmg
hdiutil makehybrid -iso -o newfile.iso yourfilename.dmg
This was found by cbro and erasei on #macosx on efnet a long time ago.