It's crazy that there isn't a "How to make Biodiesel" Instructable on the site, yet. I just created this group, but I'm inviting people to share info and links, here.
Luckily, there are plenty resources online on how to brew your own biodiesel. The stub for the Make article on the subject doesn't include the full text, but it does include a number of great links:
The Energy Self-Sufficiency Newsletter - This article is partly based on a series of articles by Maria "Mark" Alovert that first appeared here.
Gly-Tek - To test for the presence of glycerin, you can use the Gly-Teck test kit, which detects leaked anti-freeze in motor oil.
Recycling Sciences - High-volume operations can buy a $31,000 glycerin-purification distiller here, which will convert dirty biodiesel glycerin into nice, clear, commercially valuable glycerin.
Mark Alovert's site
veggieavenger.com - Homebrewing forum.
biodiesel.infopop.cc - Another homebrewing forum.
biodieselnow.com - Biodiesel policy and activism forum.
journeytoforever.org - Biodiesel processor designs and other info.
nbb.org - Biodiesel stations and industry info.
tdiclub.com - VW diesel forum.
propelfuels.com - Setting up a commercial biodiesel pump in your town.
Alternative Energy Videos - Videos about alternative energy, including biodiesel, available for rent from technicalvideorental.com