It depends on which state you are going to do the driving in.
http://www.usa.gov/Topics/Foreign-Vi...-Driving.shtml
http://canberra.usembassy.gov/resour...l.html#license
I know that in Italy for years no one seemed to care much whether I had an international license or not, till one night when a nasty cop pulled me over and asked me where it was (I'd left it home). I always have one just in case there is an incident and insurance issues arise (like the insurance company not paying out because I didn't have the proper license).
I'm told one weird thing about driving in the USA is when one comes to an intersection which has Stop signs on the face of the intersection, that is four Stop signs where we would only have two and a clear path for one road. Treat it like a roundabout.
Regards,
Renato