3 of my friends and i built one, because physics is boring and we need to apply ourselves somehow... Stood almost 20feet tall and here are the links to the video
http://physweb.mnstate.edu/phys200/PumpkinLaunch1.mpg
http://physweb.mnstate.edu/phys200/PumpkinLaunch2.mpg
only launched it about 150feet, next year, gas powered!