B-20 is 20% bio, 80% normal desel. The USMC is supposedly switching over to B-20 if not already, but soon. B-100 is 100% biodeisel. As Armdlbrl stated, the biggest difference is in the fuel pump, and I'm guessing it is because the biodiesel is a bit thicker. I've heard bio not only lubricates better, but doesn't have any sulphur to worry about building up. Daimler-Chrysler announced they plan to sell cars next year that are rated to run on biodiesel, and there is already a diesel version of the Jeep Liberty sold overseas. I've heard it can be produced by mixing lye and wood alcohol with vegetable oil.
SVO (straight vegetable oil) is completely different than biodiesel, and is fryer grease with the hush puppy and french fry remains filtered out. SVO requires some heating to get it to flow real nice, and this heat can be provided by heating element or from a hose off the radiator. You start the engine on regular diesel, then switch over to SVO when it 's warmed up. I've read the exhaust smells like french fries. When you are within 5 minutes of your destination, you switch back to normal diesel to ensure there is no SVO in the fuel lines or injectors that may clog the works. Fast food places must pay for disposal of used veggie oil, so it shouldn't be a problem to get it for free. All you need is a way to strain the crud out of it.