NeilG,
Divorcingjack has touched on the requirements. If you are also converting a Multli IFR you are required to take a minimum of 15 hours training (10 sim & 5 twin) and the flight test fee is nearly 600 quid (that's pounds not dollars !!) !!
I've just got my last set og results through, and I don't know how (well maybe I do ........ thanks Bristol !!) but I've pased all 14 exams !! It took 12 months and believe me it's a total frickin nightmare, so think hard before converting !!
Good luck !
CG