dbmartin: it's actually somewhere in between. After you've passed your medical, you'll get a nice mail with the contract from EC - you sign it and return it along with the requested documents. A bit later you'll get the invitation for the training.
As for your other question, let me quote:
"In the even of the Student Air Traffic Controller unilaterally breaking this agreement, he/she may be called upon to pay the Agency, by way of indemnity, all or part of the costs borne by EUROCONTROL in respect of the periods of instruction and probation."
Anyway, if you're doing well on the training, you wouldn't wanna do that, believe me
