This was an idea I had when fiddling with the balloon car. I spent the day thinking about how to make it instead of going out to buy new balloons, so I haven't actually tested it with a good balloon, but sticking a straw in the inlet and blowing spins it up pretty fast and makes a cool turbo whistle sound.
UPDATE: I actually bought new balloons! 12" "helium-quality" party balloons. They spin the turbine, but they have larger necks so you have to hold the balloon in place and there is some leakage. I'm working on a version 2 with a larger inlet, as well as a larger diameter output shaft.
UPDATE 2: Version 2 is here, and you can see it work! http://youtu.be/8Q6svYMZowU
It only runs for about 3 seconds, I'm assuming that's because I opened the inlet up? Maybe because I don't want to pop a balloon this late at night again. Sounds cool, though.
Measure the necks on the balloons you're going to use. If they're about 10mm. print all the parts that don't have a 2 in the filename. If they're closer to 15mm, print version 2.
Run a drill bit (13/64 in or 5.18 mm) by hand through the hole in the housing, then slide the pin through the rotor, fit it into the housing and clip the pin on the other side. The clip down't seem to stay put, but I haven't has it come off and send the rotor flying either. Glue it in place if it bothers you.
If you've downloaded version 2, you might not have a drill bit big enough (it'd have to be a bit over 10mm), so clean up the hole and the pin with sandpaper instead. The clip seems to fit better.
If you want to be really cool, you could design some sort of machine or vehicle around this. It's already got peg sockets to snap it in, you'd just need do design a new pin that works as an output shaft.