I would have thought the best idea was to try  to guess the active. If you are flying in calm air, then it will be the best ILS equiped runway.
Hang on, just remembered! If you don't have FS navigator, then get it. ( www.fsnavigator.com ) Otherwise, go onto map mode (View Menu?), click on the airport you are going to and note the ATIS frequencys. Open your radio stack (Normally Shift + 2) and tune the frequency into the COM1 radio. Flick it from backup to main, listen to the broadcast and you will hear somthing like 'landing and departing Runway 12, aproach in use'. Thats the runway.
Hope I help, Dan G