Basically you use the software that comes with the stick, and take the letters from the keyboard layout for the commands you want, and assign them to the different buttons on the X45. Example: the "N" key fires both your primary and secondary weapons at the same time. You assign the trigger the function "N." It's more difficult than it sounds.
OR...if you look around on the boards, you can find postings by EAGLER. He has been kind enough to share a file with his stick settings in it. I took his, opened it up to see how it worked, and adjusted some things to my personal preferences. (I would put mine on here for you, but I'm not quite sure how to do that...)
Best of Luck!