Matty31,
JAA ATPL ground school is usually about 6 months long. Would be nice if it could be done in a week.
If it's a week long course, then that's probably a brushup week for a distance learning course.
There's not necessarily anything wrong with taking FAA ratings, then doing JAA conversion, but I would take issue with an FTO that misrepresents what they are offering if this is the case.