B777 Captain experiences center hydraulic system failure during approach and continues to landing. After clearing the runway; a tow is requested due to the failure of nose wheel steering.

Narrative

On approach to the runway; we received EICAS messages indicating a possible failure of the Center hydraulic system. I elected to continue the approach to a landing; realizing that nose wheel steering might not be available for all or part of the rollout. Touchdown and rollout were normal and with a high speed taxiway available; I elected to clear the runway due to poor weather conditions; volume of traffic; long holds for approach; and only two runways available. Some steering was available and the runway was cleared. Tower was informed of our situation - stopping the aircraft and inability to taxi further. They also dispatched ARFF who arrived within one minute. I coordinated with the ARFF Commander while the Relief Pilot talked to Operations to coordinate a tow and the First Officer remained with Ground Control and made a preliminary PA to the passengers and ran checklists. The ARFF commander confirmed a leak of fluid around the nose gear with no other problems noted. The tug arrived within 10 minutes and after their inspection which confirmed the hydraulic leak; we were hooked to the tug and towed to the gate. No further problems were encountered. No emergency was declared due to our position on approach and proximity to landing. Tower's query as to the desire for ARFF was timely and appreciated.