Is this too much?
 

Planning on flying into Cologne for 2 nights
Travel by train to Nuernberg for 1 night
Travel by train to Munich for 2 nights.

Realistic or stay in Munich 4 nights and Nuernberg 1 night??

Hope you have better luck on te trains then I had. Just cannot understand their fare structure especially when the ticket machines are only in German.

If you need information on trains in Germany, you might catch more attention if you mention that in your heading.

First of all, to settle your train schedules and costs, go to www.bahn.de. There you can get an English version for your itinerary. Not sure if the cities are also in English,otheriwse for Cologne enter Koeln, Hbf (Hauptbahnhof = main station), Nuernberg, Hbf. Muenchen, Hbf.

Plan on leaving Nuernberg late afternoon or early evening on the day after your arrival, then one night is enough.

For your trip from Nuernberg to Muenchen buy a Bayernkarte. You can get this at the station at the ticket counter any time after 9AM. It is good until 3AM the next morning. It costs about EURO 25 which is probaly cheaper than a point to point ticket.If you are a senior, you can get the Bayernkarte for less than that. The German word is Seniorenkarte. If you are not traveling alone, the ticket is good for up to 5 people traveling together on one ticket. 4 nights in Muenchen is OK. You may want to see the city center, visit the Olympia Tower, the Nymphenburg Place, the Deutsche Museum (everything from a coal mine to full scale trains,planes,musical instruments, you name it)Be flexible in your plans and on a clear day take the train (and Bayernkarte!) to Garmisch and from there the Zugspitzbahn to the top of the Zugspitze, Germany's highest mountain. or take a day trip (with Bayernkarte!) to Salzburg.

Do not stay in Munich more than 2 nights. You will find there is not that much to do and your time is better spent elsewhere.

Might I suggest salzburg?!?! Only 75 minutes from Munchen and a LOT more interesting!!

Is there a reason you want to spend two nights in Cologne and only one in Nuremberg? I'd do it the other way around. Nothing against Cologne, but there is more to do (IMHO) in Nberg than in Cologne.
If you have no particular hotel preferences for Cologne and aren't looking for high end, you might find it practical to stay at the Ibis/Cologne railway station. It's *in* the station, very close to the cathedral, and would make it simple for you to catch a morning train down to N'berg.

Thanks everyone, especially Treplow. I'll keep my itinerary as is. Can't wait!

From the looks of Germany, I don't think you could stay long enough to see everything...it looks absolutely beautiful!!