I don't know how happy the ipad is with java but perhaps you could make some mods to the arduino software so that it has bigger buttons and is able to be used with a touch screen. It will certainly not be as easy as with an old pc to set up as the input system on the ipad is based on buttons and predefined values and not for large scale text writing. It would be like cutting a steak with a spoon.
You would be better selling the ipad and just getting a netbook with windows 7 installed... And you would get change too! Failing that , you could even get a windows tablet pc which WOULD run arduino software quite happily but you would still run into the input issue I described above...