How will the book be distributed on the iPad—on a tablet app, or with PDF? If you're doing this with Adobe Digital Publishing Suite, ask this in the DPS forum.
If it's DPS no. There is no native search available.
You'd have to do the entire thing in HTML.
it is supposed to be a tablet app...
And to Bob, it is through DPS, so I will try to figure out a solution. Is it possible to add the text search field in eg dreamweaver after InDesign has done the most of the job?