First get the ATP Prep book either from ASA or Gleim, review all the questions by yourself at least you'll be ready to take the written test as soon as you set foot in the US.
Depending on where you live in Europe, you may even be able to take the exam in your country. Get you medical as well here, list of examiners on the FAA web site (
www.faa.gov).
In the same time that you review your written, apply from your place as TSA approval may take a month or more to get depending on your background/country of origin and ethnicity, sad to say...
Then I would recommend "All ATP's"(don't have their web address now, just make a yahoo!search). They have several locations across the US, and have a very structured program to make you take the flight test quick.
If you are current on instrument, it won't take you more than a couple of days. That's an easy ride....