If I remember my regs correctly from my instructing days in the US if you are a helicopter pilot wishing to instruct in helicopters you do not need an IR. I'm assuming that is where the confusion arose.
However, for an aeroplane insstructor you need the CPL/IR as mentioned earlier.
Re-instructing, I recently heard from a good source that as the airlines have suddenly bumped up all their requirements hour wise it is a good idea to build hours before applying for a job. However, airlines will look more favourably on someone who got their hours instructing or flying cargo etc. than someone who spent $x on 100s of hours in a twin, joyriding around America. Money spent on an instructor rating is money well spent.
