With knowledge and access to Max 6 and Flash CS5, I have also designed a few applications.
This is something I build for personal use. The gauge is based off "E" being 13 gallons. Moving the needle allows will tell the program how much fuel you used under the "Gauge Reading" section. Enter the amount of miles you traveled and press the red button for your MPG. The second unit is safety reading where the miles traveled stays the same but you enter the gallons your fuel pump says when you fill up. Pressing the red button under "Average" will show an average of the two numbers.
This is a multi-menu application including home, forward, reverse, and back buttons as well as clickable boxes, words, and more. Each layer was designed in Photoshop, then compiled in Flash. Here is a screenshot of the home menu, and one shot from the timeline itself.