Collaborative Biodiesel Tutorial: The place to start if you need to get up to speed with homebrew biodiesel.
http://www.biodieselcommunity.org

The National Biodiesel Board: General information on biodiesel and regulations.
http://www.biodiesel.org

The National Renewable Energy Laboratory: Much information for the research minded.
http://www.nrel.gov/vehiclesandfuels/npbf/feature_guidelines.html