Medium Transport; Low Wing; 2 Turboprop Eng
Distraction
Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Human Factors
We were taxiing out for takeoff on Runway 1C.  This is an unusual setup for IAD.  They normally use the east runway; 1R; for takeoff but it was closed this day.  As we were taxing out for takeoff; we started the taxi checklist.  ATC interrupted that by telling us to switch to Tower and they actually gave us the wrong one and then called us back to give us the right frequency.  After that we completed the taxi checklist.  We were the only ones out there but neither of us felt rushed.  After takeoff; we turned to a heading of 340 per Tower instructions and after contacting Potomac Dep.; they told us to proceed direct to ZEHRN but we didn't show that in the FMS - we showed HEFLN.  After giving us direct to JERES; they told us that HEFLN was used for Runway 30 departures.  I double checked the fuel page and sure enough we had Runway 30 selected.  While there was no deviation; it could have been serious if this was a true RNAV departure - they use headings off all runways at IAD.Whenever a checklist is interrupted; especially more than once as this one was by the two different ATC calls because of the wrong Tower frequency given to us; it is imperative that the checklist is restarted from the beginning; not picked up from where we left off - because you may pick up at the wrong point as we did.  Also; we must verify the runway in the FMS with the heading and the runway number as we line up on that runway.
Distracted during the Taxi checklist; an air carrier flight crew failed to set the proper takeoff runway in the FMC. The error was caught when ATC issued clearance to a fix that was not in the FMC.