The train will depart from the "Fernbahnhof" about 200 meters behind Terminal 1. The train station is a three-level layout and rather compact. Also, there's good signage leading to it from any point in the airport, and it's easy to find. Just make sure you go to "Fernbahnhof" as there's two train stations in Frankfurt airport: the regional trains depart from beneath Terminal1.
I'd suggest you take the shuttle bus to Terminal 1, walk over to the train station and meet your friend right there. You will need about thirty minutes to get to the train station from the point where your baggage appears on the belt. It's a bit of a long walk, and a good deal of pain with lots of baggage (think long escalator rides). But two hours are definitely enough. Even with a ton of bags and a dog, getting to the train station from the gate at T2 takes me under an hour. Customs and Immigration are usually very easy.

Are you traveling in First Class on the train? If yes, just meet at the DB Lounge located on the mezzanine level ("Ebene 2", take the escalators one level down) of the train station. If not, meet at the Reisezentrum (DB ticket counters) located right across from where the walkway to the terminal terminates.

There's a map of the station area on the German DB site: http://www.bahnhof.de/bahnhof-de/Fra...rnbahnhof.html