I am trying to index a historical reference book and I would like to create three separate indexes - 'People', 'Places' and 'Dates' is this possible and if so how?

This is a combination of two fields: The Index Entry (XE) field and the Index field. You may need to edit them manually. Each part needs a different identifier in the entry fields. The different indices need different identifier switches.

I believe that to edit fields you would use Opt+F9. You may also need to display hidden text. Cmd+* (Cmd+Shift+8)?

(I do not use a Mac, so the keyboard shortcuts are a guess.)

Yes, this should be possible, you're going to need the /f flag in your indexing fields. This website has been a good resource for me, though I have not attempted multiple indexes yet.

http://taxonomist.tripod.com/indexing/wordflags.html