I am just halfway into doing the FAA > JAA conversion, also living in Austria.
Some things you may want to consider before you jump:
Austrian flight schools (and the Austrian CAA (Austrocontrol)) do NOT LIKE conversions. They prefer selling their 60k ab-initio ATPL packages and not bother with the pain of people who did their training in the US.
I spent 4 months doing e-mails, letters, phonecalls and visits at most of the FTO's in Austria, plus spent what feels like 400hrs on the phone with Austrocontrol, and the conclusion was:
Apart from one FTO in Salzburg ("flighttrack"), none even WANTED my business!! They said they know too little about the process, or said they are too busy with their integrated courses. Basically told me to go
OFF!
Second thing to consider: The cost!
A poster above said you should expect spending about 15,000, that sounds about right, but can be more if you do not pay attention to details.
IMPORTANT IS: Even though all JAA memberstates should follow JAR-FCL (the equivalent of your FAR's, as I am sure you know), every country is given a lot of leeway in making some own rules into it.
For example:
Switzerland: No retraining required
Austria: Retraining as FTO deems necessary
The UK: 15hrs instrument, 10 in a FNTP II sim (if I recall that correctly)
etc...
Make sure you get in writing what amount of retraining you have to do before you enroll with them, don't let anyone screw you with that. 10hrs multi-engine cost a small fortune in Europe, compared to the States.
Next on the list:
Staying fresh!
I can assure you you will miss the flying extremely!!! You have to pass all 14 JAA ATPL exams before you can go for the checkrides for the conversion!
The exams are some 14,000 questions in total (compared to 1,300 in the FAA ATP exam), so it will take a great deal of self-discipline and time-management to get it done in say six months).
During that period, you can not fly in Europe - at all! There may be the odd FAA registered aircraft around to rent, but from my experiences these people know exactly what they can charge for them, and most are even more expensive than their JAA equivalents. Not worth it!
If you can, enroll in a ATPL theory distance learning course, and study all the material in the States while you can still keep flying. Do not expect to know most of the materia already, as 80% of the theory there is useless for flying. Most of the stuff you will hardly ever need again - it's a challenge basically.
In the end I am sure it will be worth it though, coming back is nice!
edit: If you care for a personal hint: Have a look at "Horizon SFA" in Zurich, Switzerland! They are probably the only flight school that offers a good JAA ATPL Theory distance learning package, because they have a "special conversion offer" for people just like us. If costs about 3000 euros in total, including all textbooks (Oxford Aviation Academy theory books). I can recommend them, however realize that if you go that way you will have to take the exams in Switzerland, not in Vienna!
(I wouldn't recommend doing the practical conversion part with them though, horrendously expensive! approx. 300 euros for 1 hr in their FNTP II sim, approx. 550 euros for 1 hr in their Diamond Twin Star...!)
If you have more questions, shoot on
