There is a version of the Rohloff speedhub that is meant for use with vertical dropouts, another for horizontal dropouts, and another for a special type of fork end that is Rohloff specific, you just need to order the model that is appropriate for your frame.

In short, if your bike is already spaced for an internal hub, there is a Rohloff speedhub that will fit it, you just might have to do some thinking to figure out which model (since they have slightly different attachment methods). A call to Harris Cyclery would solve your problem, and you should look over their webpage on the speedhub: http://www.sheldonbrown.com/harris/rohloff.html

peace,
sam