[citation][nom]kingnoobe[/nom]Actually shuff you can use vegetable/peanut oil to run a diesel engine with slight modifactions. It really doesn't cost that much. You can take the used oil from mcdonalds..etc and simply filter it to make it useable. And it isn't that hard to do. It's simply a matter of straining it very good to make sure to get all the grime out. The problem is it pretty much has to be used oil. Otherwise you'd spend more on the oil then on regular disiell or gas[/citation]First of all, that is NOT biodiesel. As the OP said, biodiesel requires considerable processing. What you are advocating is SVO (straight vegetable oil) - worse, you're advocating using used oil with only minimal filtering (screening).
In order to use SVO, you need to do an SVO conversion in most cases. Furthermore, SVO will significantly reduce the lifespan of a diesel engine! Properly prepared biodiesel, on the other hand, shouldn't hurt the longevity of a diesel engine. Especially if you're using a biodiesel blend.
Oh and cold weather? Forget it. Even properly processed, cleaned, dried, cold-filtered --biodiesel-- STILL requires blending with winter diesel and/or keresene to avoid gelling at very cold temperatures. Nevermind most SVO batches, some of which would probably start gelling at near-room temps. Plus, I hope you like changing your fuel filters often - did I mention recent model diesels often use multiple fuel filters and they're quite expensive?