trains from Munich

Use the German Rail website, http://reiseauskunft.bahn.de/bin/query.exe/en, to get schedule information. It helps to spell the towns correctly (although you can us ue for ü, or just u). Munich to Salzb u rg takes about 2 hrs via the regional trains you can ride with a Bayern-Ticket vs. 1½ hrs by the fastest, most expensive trains. ICEs make the trip to Nürnberg in just over an hour (but you can't use them with a Bayern-Ticket). Some ICEs go non-stop on a special high speed track. There are also Regional Express trains from Munich to Nuernberg. The time varies with the route. Every two hours one takes the same fast track as the ICEs and makes the trip in 1h43m. The fastest regional connection to Rothenburg odT takes 3¼ hr with train changes in Treuchtlingen and Steinach.

Is it easy to get from Nuremberg to Rothenburg? Can we possibly hit both of those towns in one day?

1 and a third hours on the train. If all you want to do is "hit both towns". If you're going to make the effort to go to RodT is worthy of a good half day or more, especially if you can be there in the evening after the tour buses have left. Nuernberg is not a town but a city with plenty to keep you going for a day or two. IMHO to attempt both on the same day would do neither of them justice. It would be a shame to go so far and see so little. But, as has been recently discussed in another thread, its your trip. Lee has given the website just above for the Bahn; if you put your travel points in there you will be able to plan exactly how to get from one to the other.

Nuremberg/Rothenberg; you cannot do either town/city justice by trying to do both in one day, and travel time. Both deserve at least a majority of the day to themselves (at least). I would be inclined to spend a full day and night in each at a minimum- or both days in one.