yep, that’s it – bahn.de can tell you everything you need to know about train services between any cities, and you can get it in english too. remember if you’re a foreigner you can get really cheap pre-purchased train tickets. you buy them before you go (or after you’re there at a major train station with your passport) and you get a book of 5/10/etc pre-paid train journeys which are valid for all but ICE (the nice, fast, expensive trains) services between any two cities. i think i paid $200 australian for 5 trips, which is $40 AUD per trip so about 27EUR (i guess?), which works out much better than buying it there most of the time. you just take them in and pre-book your seat on any service.
there’s information on the bahn.de site about these, but you can also ask your travel agent as you have to purchase it through them anyway.

have an awesome time!! the dom is incredible, avoid the shopping district as it’s a LABYRINTH and if you’re distracted by shiny things you’ll never get out :-) and if you’ll be there (or in the area) in february, make sure you see Karneval – just incredible.

cheers :-)
eks