Dude if its not a heater hose running allong the fire wall it could be that your inlet manifold gasket needs to be replaced.I had this exact same problem with my R33 GTS-T i couldnt tell where it was coming from untill i stuck a torch and an extendable mirror down there.It was the coolent chamber closest to the fire wall the rubber on the gasket had worn away down to metal and was leaking water.I didnt rule out the fact that it could have been a coolent hose running to the inlet manifold to the turbo allong the rear of the engine that and the heater hose beacause it seemed the most viable untill i could get a a closer look with a mirror........
From looking at this picture it looks like all you have to do is remove throttle cable disconnect fuel lines from fuel rail drain coolant remove top heater hose unplug any hoses and cable blocks (inc injector harness) that are connecting to the plenum .give yourself some room. remove the fuel rail with injectors after this you should in my theory be able to undo the plenum from the side of the block if there are any hoses connecting underneath the plenum then you can give yo self more space by pulling the plenum off and lifting it unitill you can get enough room to disconect them.............Theres a few things that you need to keep in mind when doing this and they are document as needed your prgress i.e.where things go(pictures help allot).dont overtighten nuts & bolts,check to see if any hoses need replacing there cheep as shit and will save you if you can get your hands on a tourqe wrench and torque tightening specs(i know for a fact there is an r32 GTR workshop manual floating arround on here).theres a few others you can do if they need to be done belt,water pump etc....All my work was done in my garage at home by myself no hoist no removing starter motor and with a basic tool set.GOOD LUCK.I hope that i was of some assistance to you.