heres what i understand:

WVO: waste vegetable oil - is used vegetable oil (as in, yesterday i was cooking my lunch in it, now im burning it in my engine) has to be filtered and congeals at a lower temperature than straight, unused vegetable oil and has to be kept warm so that it will be able to flow throught the fuel lines and the IP, but is essentially free and easy to find.

SVO: straight vegetable oil - new vegetable oil, corn, soy, peanut, canola etc. requires no filtering because its new, is fluid and only has to be heated in colder climates, but is expensive.

Biodiesel: either one but with a chemical additive so it requires no conversion and is commercially available in some places.

Another thing i read about but have not heard mentioned in this forum is GTL:
"Another intriguing alternative to oil comes from natural gas. Gas-to-liquids (GTL) is the clunky name given to a set of fuels that can be blended into conventional diesel and used in today's engines. They have the advantage of being super-clean, as well as boosting the potency of diesel fuel. Though they can be made from coal or biomass, the most likely option is natural gas." - The Economist April 28, 2005

My questions:

Is what i said above correct? what fuels can I use that require no conversion at all? how warn do SVO and WVO need to be to keep them flowing? what is this GTL and is anyone using it? can it be blended into WVO/SVO instead of methanol to make biodiesel? can any of these fuels increase maintenence or shorten engine life?

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1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350