I did this about a year ago, and if I remember correctly there is a bus that leaves from just outside the NCE terminal that goes directly to Cannes and leaves you off at the main bus square (directly in front of that Festival theatre and the harbor). To get to the Hilton, make a left and walk along the Promonade (the harbor is to your right as you walk) about 5 blocks. You can't miss the Hilton, it kind of looks like something that would be very much at home in an Austin Power's movie! I'm sure the hotel can tell you the bus number or if you look on the airport site it should be there as well. I agree you really don't need a car, Cannes itself is very 'walkable', and if you want to visit some of the neighboring towns, the train is the easiest way to do so. You can take the local train all the way into Italy (Ventimigilia) or get off in Monaco, Nice etc.