What about running ubuntu (live cd or installed) on one of your intel machines and copying the powerpc iso on to usb from there? Linuxopjemac will tell you it doesn't work, but I can't see why not personally. The dd command just copies raw data afterall. See my posts on the link I gave you earlier for instructions.

Have you checked the checksums for the iso like on the other links?

Sorry, can't be much more help. Have never used a mac os!