How do you correct for viscosity when using vegetable oil in a diesel?
I once had several sites that discussed used cooking oil as a fuel but they have long ago dissapeared into cyber space due to a computer crash.
BTW I have recently heard of 4 new soy diesel plants being constructed here in SE Iowa.
I remember sitting here argueing with several old timers about the feasibility of alcohol and biodiesel as motor fuel. Several thought the cost of gasoline would have to reach $5.00 a gallon here in the states before it would be time to start producing biofuels.
I wish I knew the smilie symbol for sticking my tongue out. 
Basically you heat the vegetable oil to make it thinner, or add a thinning ingredient, or synthesise biodiesel out of it. Journey to Forever have a lot of information on this.