We need to be in Windhagen, Germany on 10 May,2008. we will be leaving Tarragona when to get there and by which train. We already have a rail pass. We have no reservations for any trains yet.
You should look at he www.db.de
It's easier to find Cologne if you write it in German, Köln. For example:
Tarragona Sa, 10.05.08 ab 15:39
Cerbere Sa, 10.05.08 an 19:02
Cerbere Sa, 10.05.08 ab 21:21
Paris Austerlitz So, 11.05.08 an 07:30
Paris Nord So, 11.05.08 ab 08:55
Köln Hbf So, 11.05.08 an 12:45
So that's an overnight voyage. For the trains Cerbère -Paris and Paris-Köln you would probably need a reservation.