You won�t need an International Drivers licence � your photocard & paper licence are all you need.
I have hired many times in the USA and normally don�t even get asked to produce the paper part of the licence.
My advice would be to organise the hire before you go and make sure you don�t get stung for insurance � check that it is included in the price quoted (just turning up at the hire desk will normally entitle you to their most expensive tariff).
Search the web for the best deals, I would recommend either Holidayautos.co.uk or Carhiredirect.co.uk � their prices are hard to beat.