We've been using Simply Accounting for our first radio station for the past year.  We did not originally set up Simply to use departments, so all of our data reflects the single radio station so far.  We now have a second station ... so we'd like to turn on "departments" and have our first radio station as Department 1 and our second station as Department 2.  Can we accomplish this without having to re-enter all of the data for station 1 assigning it to a department ... can we simply "export" all the existing data to Department 1 and start adding new data for Department 2?

You cannot 'export' the data over to 'Department 1'.  When you turn on the departmental accounting feature, the existing data will show up as 'unassigned' in departmental reports.  Moving forward though, every entry can be allocated to a department.