Don't know about helos but for normal aircraft the instructor rating covers you for aircraft within a class e.g. single engined piston but then to teach on a particuler type you need to have flown 5 hours in it (probably P1 but can't remember).
You could try searching the JAA website at
www.jaa.nl (I think).
[ 17 November 2001: Message edited by: DB6 ]