Biodiesel is, I believe, the vegetable oil and whatnot, with the modifications already done to the fluid to allow it to work in a stock system. Biodiesel's already out, usually mixed 80/20 with petroleum-based diesel fuel.
Again, I'm not sure on the specifics, except that you don't need to to modify the car at all to run on BioDiesel.
Also, what's the paper on, exactly? I wrote a paper comparing diesels to g@$$ers a year or so ago, if you'd be interested in taking a look at it...
