Just came across this while reading one of my favorite blogs - Make (all about making stuff). You can purchase a dvd that shows you how to convert your standard diesel powered vehicle to one supplemented with used vegetable oil at http://vegmyride.tv. For $19.95 they show you how to run a duel-tank system (meaning you still have your factory installed diesel engine and tank) so you can still run on standard diesel whenever you please. They figure that by running on used veggie oil your cost per gallon is $.15. Wonder if your exhaust smells like french fries. Man, that would be cool. :)
It isn't a Michigan-based company, but the concept is too cool not to share. Especially when gas (and diesel) is $3 a gallon.