I expect many people are familiar with this software, but I didn't find any previous threads in a search so I thought a post about it might be useful.
What this great (and really easy to use) software does is to allow multiple input devices (e.g. two keyboards) to be recognised as individual controllers in the flight sim. Within the software, each piece of hardware gets a name eg keyboard1, and then each button / wheel / etc can be programmed to a flight function within the sim. Using some creativity, this allows for very nice looking bits of flying hardware to be made for pretty much nothing.
I've just started with it, and have made a trim controller: I took ball out of a really old usb mouse with a scroll wheel. The wheel was in the middle between the left and right buttons, so it became the elevator trim, whilst the buttons were set to rudder trim. I will be spending some making it look a little realistic, but for now it's just taped to the side of the desk D.
It's freeware and can be downloaded here: http://hidmacros.medek.info/news.php
First Officer