Two weeks in Germany

Basically, you can use trains or drive. You "are hoping to do some traveling within Germany but are also wanting to travel to a few other countries like France, Switzerland and possibly Poland and wherever else we can visit." From Frankfurt, ground travel to Poland is going to eat up much of your time. With two weeks, a more realistic trip would take you into France and Switzerland. Paris is about 4-5.5 hours away depending on which train you use. A one-way ticket for 2 costs 98€ from Frankfurt on some departures. Check your dates: http://reiseauskunft.bahn.de/bin/query.exe/en Or consider a trip south to the Black Forest area. You'll be within striking distance of both France and Switzerland this way. Stay in or near Freiburg, and you can easily daytrip to BF villages to Colmar (FR) and Basel (CH). Or stay in Gengenbach, an old walled town similar to Rothenburg, and do daytrips to Strasbourg (FR) and to BF villages along the Black Forest Railway: http://www.black-forest-travel.com/places-of-interest/black-forest-railway.html You can get to Freiburg or Gengenbach in about 2 hours by train. It'll cost about 50€ - 70€ each for regular tickets. Slower regional trains can be used too; for these, there are small-group daypasses that will cost less than 50€ for two. Train travel within the BF area is free if you stay in a town like Gengenbach: http://www.blackforest-tourism.com/konus If you want to travel more widely and not be bothered with individual tickets, a FR - CH- DE railpass will cost $800 - $900 for two for 5-6 days of travel: http://www.ricksteves.com/rail/select.htm

With only two weeks you're probably not going to have time to go to that many different countries. I would try to focus on Germany and either France or Switzerland. Your best option for France is exploring the Alsace region, as it's right across the border. I think the train is the easiest way to get around, but if you want to see some of the smaller towns and do the wine road in Alsace, you'll want a car.

You could do a little loop, down to Heidelberg, Strasbourg, up to Luxembourg, Trier, then around back to Frankfurt. It depends if you are just starting and ending in Frankfurt and want to travel somewhere in between or if you want to only day-trip from Frankfurt, being back there every night.

Ashley: It's just too easy to take on too much on a 2 week trip, and it can all easily be a blur. With $9 gasoline, travel city to city is best done by train. Local city travel is by mass transit. Central locations let you do day trips by rental car. France is such a large place, and it would require a trip to Paris.
Poland is pretty far northeast, and it would require quite an effort to visit. You don't want to spend all day, every day on trains. The trains out of Frankfort go up the Rhine River toward Amsterdam. Great stops are Bacharach (south of Koblenz) and Cologne. It's a beautiful area. Trains also go south toward Switzerland, and this would be a good direction to go. You could come back east through western Austria and staying in Innsbruck and Salzburg. Munich is closeby Salzburg. Trains back to Frankfort from Munich would be easy. This route alone could take up much of your trip. I'm off to Tuscany and Rome for Easter. My next European trip will be Vienna-Budapest-Prague, which is a 10 day trip into itself. Just try not to bite off more than you can chew.