Pretty much what Irv said above. Different rules depending on whether you have less than or more than 100 hours. You can also check out his website which has a useful Q&A if neeed.
Lasors can be downloaded at:-
Lasors 2004
Questions you need to ask though are:
- why convert if I plan on training for professional licences?
- can I get access to a "N" registered aircraft where I intend to fly or hour build - in which case why get a JAA ppl