Going to Frankfurt for a vacation in the spring 2010. Have been hours on internet trying to figure the types of connections for trains and buses as well as arr/dep schedule and cost. This seems to be a real challenge. Have never traveled either way and need some help evaluating the best course of action. We would like as direct a connection as possible as well as the duration. We don't know now where we will be staying in Berlin but I take it that there are many arrival and departure points in each city. If there is a site that could give me this info please let me know. I did get some info on Eurorail
and found it to be very expensive.

It's a 4hr train ride from Frankfurt to Berlin. Departures every hour all day at :13 past. See www.bahn.de. Schedules for next spring may not be posted yet, but they will change little to none from current schedules. Fares start at 29 Euros. Limited tickets, you should have no trouble getting that price if you buy far enough in advance (once they offer them for sale)

You can't get there faster or cheaper by plane.

Have you checked www.bahn.de ?

There are direct trains (ie, no change required) every hour; journey takes 4:08. If you buy your ticket online (via DB) in advance, you can get them for as low as 29 euros 2nd class ; 49 euros first class. These deeply discounted tickets are only good for the specific train you booked on; and are non-refundable.

If there's more than one of you traveling together, the discounted fares are even cheaper: 49 euros for 2 people in 2nd class and 79 euros for 2 people in 1st class.

If you buy tickets at regular fare, it is 111 euros per person for 2nd class.

P.S. The regular fare tickets are fully-refundable, which gives you flexibility. That's why they're so much more expensive.

As the others have said, book well in advance (up to 90 days allowed) at www.bahn.de to get discount fares.

The direct trains depart from Frankfurt Hbf and arrive at Berlin Hbf. Hbf = Hauptbahnhof (main train station). On the DB site the Frankfurt station is listed as Frankfurt(Main)Hbf. "Main" is a reference to the full name of the city, Frankfurt am Main, to distinguish it from other cities named Frankfurt.