i don't have a QX4, but i do have the '01 pathfinder. the brakes should be the same. thanks to fueler, he provided me with this link to help service the bearings. you might as well, since you're already there.
i would suggest new grease seals which hold the inner bearings in. if you have ever replaced brake rotors and pads, removal and installation is easy. the hardest part is separating the hub from the rotor. i had to flip the rotor upside down, prop the rotor up, between two pieces of wood. i used a 6" 1/2 drive extension to hit the hub from the rotor. you have to smack it hard and move around the parimeter. it will separate.
i know the link is for the Xterra, but trust me, it works !
http://rkrenn.com/xterra/howto/bearing/bearing.htm
good luck .