A B767-300 CFTT occurred during an approach to JFK following a long and tiring trans-oceanic leg. An incorrect altitude was dialed into the MCP and no one caught the error.

Narrative

As First Officer I was flying pilot. [We were] arriving early in the morning [at JFK]. While on vectors for the ILS 31R at 3;000 FT; ATC asked us if we had VFR arriving traffic on 31L. After sighting the 31L traffic and the airport we were cleared for a visual approach to Runway 31L. As the FMS was updated and the ILS frequency selector was changed to Runway 31L by the Captain and Relief Pilot; I mistakenly changed the Mode Control Panel (MCP) altitude selector to 100 FT instead of the glide slope intercept altitude. When ATC advised us we were below minimum vectoring altitude (approximately 1;000 FT AGL) I climbed back to the glide slope intercept altitude for Runway 31L. The remaining visual approach and landing were uneventful. I believe contributing factors for the mistaken MCP altitude change are as follows: 1. Late runway and approach change. 2. Fatigue caused by early morning arrival. 3. End of a long transoceanic leg that included extensive intra-African operations; weather and track change. 4. Marginal VFR. 5. Mistakenly incorporating elements of an RNAV approach procedure with common visual approach w/ILS backup procedures (MCP altitude window change).