B757 Captain reports his First Officer descending below 4;000 FT prior to MISCH during the ILS 14R at ORD.

Narrative

While [we were] on arrival into ORD; we were given radar vectors to intercept the ILS 14R final approach course; and to 'maintain 4;000' until established; cleared ILS 14R. We intercepted the final course just inside BIFLE Intersection. Approaching MISCH the First Officer; who was the pilot flying; wanted to continue descent below 4;000 FT. The charted altitude at MISCH was 5;000 FT and we were IMC. 'I said no don't descend yet until MISCH.' The First Officer said the altitude at MISCH was (charted) 5;000 FT; I looked down at the chart and saw note 3 which said '2;500 when authorized by ATC.' At this point we were getting very busy talking to ATC and configuring the aircraft further for landing. When the First Officer continued to descend prior to; but very close to MISCH; I did not intervene further after reading note 3; but then I regretted that after further review of the ILS 14R chart. We passed MISCH at approximately 3;600 FT MSL; and continued in for a normal landing. After parking at the gate; I debriefed the First Officer that I believed we should have stayed at 4;000 FT until the next charted segment; which meant waiting until passing MISCH; and then descending to 2;400 FT and intercepting the glide-path at that point. I believe the First Officer wanted to descend ASAP so as to pick up the airport visually for landing. We were cleared for the ILS in IMC conditions; and clearly we needed to stay on the charted segment until the glideslope intercept point. I will be very proactive in the future to insure this does not happen again.