Its fairly involved, but not too bad... Its been a while, but it was the first real mechanical work I'd ever done ca.1998... A Chiltons manual is very helpful. I used the big book for imports 1980-1986.
Get all the extraneous crap out of the way. That airbox tube and the brackets and the fan shroud. Break the crank-nut free first, because it will help lock up the motor. One time I locked up the belts using bungee cords just so I could break the crank-nut free. Pull the fan off (four 10mm nuts, I believe). As I recall, the accessories can stay in (alt steering pump ac), but of course, their respective belts must be removed. The timing covers have Philips headed machine screws around them. Use a puller for the crank pulley, and take off the bottom cover. Keep the rubber seals for the timing covers attached to the covers. The book will tell you to put the motor at TDC for cyl #1.
Mark the sprockets before you remove the belt. There are clear markings on the sprockets that you will want to locate before the tensioner is loose and the belt is removed
You'll need an Allen key for the tensioner. I think its 7mm, but I really can't recall.
Once the timing belt has been removed, DO NOT rotate the engine or turn either of the sprockets
I recommend changing the water pump/fan clutch at this point because something timing-related is in the way of the pump, as I recall. Its an extra hour or two cleaning everything and draining coolant, but it'll save you several hours down the road.
I also recall that the new belt comes with white lines to line up on the sprockets. I think the crank sprocket is around 4:00 and the cam sprocket is at 12:00, but the book has a couple of pictures to guide you. Put on the new belt and let the tensioner do the work of tensioning. Nudge the crank pulley clockwise(maybe a tooth or two) to take up the slack in the belt while the tensioner tensions, and then tighten the Allen key in the center to lock the pulley.
Reassemble and enjoy!
Always use geniune Nissan parts!