These guys are using an EPIC card to interface the buttons, switches, LEDs and rotary knobs with the computer. Then there is another program called FSUIPC that is required to interface with all the varialbes in FS2002. The Project Magenta software is set up on different computers. For example, you might have one computer running FS and a second running the PM software like a PFD, a third running a ND, a third running the MCP software and a fourth running the FMC-CDU software. All the computers are networked to get the whole project to work. It is really an awesome hobby to have thanks to a small group of hardcore developers out there.
I have a PPL and still view FS as a really cool tool to practice procedures and checklists. Once I get the room cleared in my house I am going to be building one of my own 744 rig. Can't wait. PS1.3 is by far the best simulator around. It only simulates the 744 but it is worth every penny. I definitely think it would be good for pilots that are early in their career to try this software and become familiar with the FMC, LNAV, VNAV, and all the complex systems on a 744. It can only help.