A pilot reported that after making the proper CTAF radio calls and while holding for takeoff on SSI Runway 22; another aircraft passed over head after a Runway 4 takeoff.

Narrative

While taxing from the FBO; the Captain (pilot not flying) broadcast our intentions to taxi to and depart on Runway 22. After completing the taxi checklist; he changed over to the #1 radio in order to contact the local Center frequency for a release to our IFR clearance. No other broadcasts were heard on the UNICOM frequency. With a release received; we continued taxing slowly forward. I looked left (as I was pilot flying) and saw no other traffic on the Runway (4/22). I turned right in order to use as much of Runway 22 as possible. With the before takeoff checklist complete; I made a 180 degree turn at the approach end of Runway 22. Completing the line-up turn; I noticed lights at the opposite end of the runway and remarked; 'That looks like another plane doing a downwind takeoff.' The Captain replied; 'Exit the runway!' Within seconds we were at the taxiway. The small aircraft had departed and was overhead around 100 FT AGL. Looking down I verified we were on the correct UNICOM frequency and then looked at the Captain. He said; 'I didn't hear one broadcast; did you?' I replied; 'No.' We re-took Runway 22 and departed without incident. In the future; we are both going to stop short of any un-controlled runway and monitor the UNICOM for a full minute ensuring no aircraft has taken our intended runway.