Hey,
Get the software from Jeppesen, you cannot fail the knowledge test if you do the course. I think its called "Commercial Pilot" and it has both courses of study (fixed wing and heli). It's about $250.
I don't know where in the UK you can do the computer test but you can certainly do it in Cork in Ireland with South Aer (
www.southaer.com) the guys name there is Scott.
If you already have the JAA stuff the FAA will allow you away with just a flight test to convert the licence, I don't think piggy back licences are allowed anymore after September 11th. The flight test costs about $250 I think too. A guy called Adam House is an FAA examiner in the UK, I don't have his number but if you want post back here and I'll get it for you.
That's all I know buddy!
