According to a list that our WOD passed around here in the Sand, Yank Rank (like that?) goes up to 5 Star (Fleet Admiral, General of the Army and General of the Air Force). I've seen the Chairman of the JCS on the telly and he is a 4 Star. Pretty sure GEN Macarthur made himself a 5 Star when he was in the Philippines.
For info, the Service chiefs in the ADF are 3-Star and the CDF (Chief of the Defence Force) is a 4-Star, hence GEN Cosgrove. Not sure if our defence force is big enough to warrant 4 Stars.
On a different note, the Yanks seem to have an awfully hard time identifying rank that is different to theirs.