B737 flight crew landing with fair to poor braking action; find braking nil at end of runway and slide off onto over run.

Narrative

On the ground in our departing city; we reviewed weather in ZZZ. Discussed and expected forecast weather conditions; low visibility due to heavy snow. I (First Officer) being the flying pilot was briefed prior to departure that I would fly and we would execute a company procedures approach. Actual visibility would dictate landing pilot. Enroute phase was uneventful. When in range; Captain communicated he was off #1 com to retrieve ATIS from #2 com. ATIS showed winds 270 at 3 KTS; visibility 1/2 mile snow and fog; 400 overcast; temp 0 dewpoint -1; altimeter 29.27; ILS XX is in use. A complete brief of the ILS approach plate was completed. We again discussed company procedures approach with visibility dictating landing pilot. Actual ATIS and weight (111;100 LBS) were inputted in landing calculations. Also selected engine anti-ice on; runway condition wet-poor and visibility less than 4000 FT. Reviewed data and determined flaps 30 with auto brakes selected to 2 was adequate. Speeds were REF 135 and 140. While being vectored for the approach we received a verbal weather update of winds VRB 3 KTS ceiling indefinite 400 FT. We were then offered the choice of Runway XX or YY. After a thorough briefing of Runway XX; we decided it was prudent to remain with Runway XX; not to be rushed for YY. We were vectored and cleared for approach to XX. Configured on schedule and was on path and speed. During approach Tower advised aircraft were rolling to the end of the runway for exit onto taxiway with fair to poor baking action. We then planned last taxiway for our exit. Broke out at approximately 500 FT with good forward visibility. We could see the end of the runway. I was instructed to take over visually which I did and immediately announced landing due to good visual references. Touched down on speed and in the touch down zone on centerline. I immediately set the nose down and deployed full thrust reversers. As we slowed to approximately 80 knots I started manual braking. Due to the manual pressure required to disengage autobrakes; I immediately sensed a skid. I remained on the brakes and stowed reversers around 60 KTS. Captain announced joining on the brakes followed by a positive transfer of controls. Apparently our speed was decelerated enough for Tower to ask if we could make the next taxiway. At a quick glance it appeared to be covered in snow with no decisive markings. Captain said no; I replied unable. We continued to decelerate to what appeared to be an adequate taxi speed. Due to the blanketing of snow coupled with the heavy snow fall; runway and runway environment cues were extremely diminished. I did not note the IRS digital speed readout; but noted airspeed indicator 0 knots. As we approached the last taxiway; the Captain executed a turn with the tiller coupled with braking. The aircraft turned approximately 45 degrees of a planned 90 degree turn. Quickly realizing the situation of not turning and not stopping; full manual brakes were applied along with an attempt of reverser deployment; no effect due to idle speed. Aircraft departed pavement at of taxiway and end of runway. Upon departing; engines were shutdown. Aircraft came to rest parallel to taxiway about 40 FT from the edge of taxiway. Executed appropriate checklists. Talked with Flight Attendants and passengers; contacted Ground and Operations. Did not declare emergency; but was never asked if assistance was needed. Airport Fire and Rescue was never dispatched to our aircraft. Operations arranged for deplaning passengers via air stairs onto airport buses. Another carrier landed immediately behind us due to interruption of communication between Tower and us. They reported braking action nil. Airport was then closed to inbound and outbound traffic. No crew or passenger injuries reported. Contract Maintenance inspection found number 4 main sliced to cord due to 3 runway end identifier lights. Also learned from the Mechanic that at least 3 prior arrivals sustained gear damage