Traveling in Germany. How often can I expect trains from Bremen to Munster.? What about Sunday schedules?

Do you really mean Munster, the village in Lower Saxony known only for its nerby military training area? Or maybe Münster (also written as Muenster)? There are 3 Münster in Germany:
1.) City in Northrhine-Westfalia with a famous University
2.) Münster in Hesse
3.) Münster in Bavaria

In general, trains are running frequently (usually at least hourly from morning till late evening) even on sundays.
Whichever Mu(e)nster you mean, you can look up train schedules and prices at
http://www.bahn.de/p/view/international/englisch/international_guests.shtml

Assuming you are talking about muenster, the University Town: Train between Bremen and Muenster takes about 1h 20 min and a train leaves every hour during the day (weekdays and sundays) and several trains at night for ~31Euros. Since the towns are fairly close there are also several other slower trains and buses but they are significantly slower and not much cheaper.

Look for the schedule on the DB deutsche bahn web site and search for muenster, you can also buy your ticket on-line

Here is the official site to look up all train schedules in Germany. Happy travels.

for more information about the train schedule look in the web
www.bahn.de

www.db.de

That should answer all train related questions for you

Why don't you just buy the Thomas Cook railroad timetable for a few bucks and you can plot all the trips you care to take.