Just in case you're curious and don't want to have to page through the manual, to turn on the HUD:
Flip all the switches that are circled in this picture:

Then click the wheel circled here:

And your HUD should be up and running like in the last picture.
Apparently, Aerosoft did such a good job programing the HUD, it's actually used as a professional trainer!
Also, I don't know how I missed it before, but that last shot is awesome (yours, not mine

).