NXTLiftBoy posted building instructions for his project on photobucket.
Also, I asked him for some additional details. Here is the reply:

MODEL
Apart from the technic pallet with the V10, the NXTLiftBoy was made from a single NXT set. I spent several evenings over several weeks to construct it. I started with a solid fork and a mast that fitted the fork. I dreamt of a mast in parts (telescopic), but thought that that would be too much to ask for. Wanting the brick as a counterweight, it took a while before i gave it the simultaneous functions of weight, backward extension and pivot wheel support. Particularly the pivot wheel was a pain. The big rotating disc/wheel in the set had too much friction, so the wheel wouldn’t follow but, at times, even bump around. A single tyre would give it a too narrow base, so it tumbled over when turning at high speed. Two tyres required the split axis, not visible from the outside. At one time, i even used a blue ball in a cage instead of the pivoting wheels i ended up with now. The ball worked well but didn’t have the looks…and the red ball neither
After getting the pivoting wheel ok, i added the cabin, chair and mirror from the remaining parts.
To my taste, the cabin and brick ended up too high, maybe i’ll have an attempt at a redesign/makeover, suggestions are welcome.

SOFTWARE
Inspired by Brixcc, and using the iCommand library, i created a Java program that enabled me to control it wirelessly with the mouse. The mouse is inside a control plane, at the center nothing happens. Moving the mouse up makes the NXT move forward. Position in the plane determines speed. Left/right position of the mouse in the plane determines the curve the NXT makes. At the edges it turns on the spot. In the center it drives straight. Halfway the edges it turns around one of its wheels.
There 200×200 ways to drive the NXT, it is a proportional controller. It sends an update every 20 milliseconds to the NXT, but only if there is a change, to save batteries.
Left/Right-clicking the mouse makes the fork go up/down.
The fork has ‘auto-accelerate’, meaning that upon click-and-holding the button, it increases fork speed from 0 to 100 in about half a second. This way you get the speed without losing precision in maneuvering.
Double-clicking the mouse in the control plane (de)activates driving. If the mouse leaves the plane the motors are stopped too. The software has radio buttons to configure the motors wiring and orientation.

Even with the custom software, it is a real challenge to get used to the controls and operate the forklift as a pro!