You can find timetables and prices here:

http://reiseauskunft.bahn.de/bin/query.exe/en

DB timetable

http://reiseauskunft.bahn.de/bin/query.exe/en

From: DUS (shortcut for Düsseldorf Airport)

From: D (shortcut for Düsseldorf Hbf (main railway station)

To: Prague

To: Munich

To: MUC (shortcut for Munich Airport)

Düsseldorf - Prague

Cheapest option would be the night train if you can get one of the cheap specials. With day time trains make two queries:

From: D

To: Dresden

From: Dresden

To: Prague

Plan enough time in Dresden as the specials are only valid for the booked trains. Easiest with a night spent in Dresden. Which is a very worthwhile a visit.

http://www.dresden.de/dwt/en/index.php

If you want a special you have to book in advance. Earliest possible 89 days before traveling. Latest 3 days in advance, but the specials will sell out normally long before this.

Prague - Munich

Buy in Düsseldorf (!!!) a Bavaria-Bohemia Ticket for the travel date you plan to do Prague to Munich. EUR 32,00 if bought from a ticket machine. EUR 34,00 if you go the counter. This ticket is good for up to 5 persons traveling together and covers the route from Plzen/Pilsen till Munich. It's a day ticket covering all regional trains in the Bavarian/Bohemian border region. However on this route there are anyway only regional trains (RE/R). The ticket covers furthermore all local public transport in Munich (S-Bahn, U-Bahn (metro), trams and buses).

In Prague buy normal tickets from Prague to Plzen/Pilsen. CZK 145 pp (~ EUR 6). Minus group discount.

www.cd.cz/static/eng/pricereduction2.htm