You don't want to convert to VOBs, that will defeat the purpose of having the movies in hi-def. Opening the ISO with Toast and then burning to disc should work. Toast is like $80.
Failing that, your only other option would be to network your Mac to PS3 with a program called Medialink. With medialink your PS3 will be able to access content directly from your Mac. Open the ISO up, and look for the .m2ts file. This is the actual video file you need to play on PS3.