I realize this is an older thread but couldn't stop myself from posting. I have an '82 N/A diesel vw rabbit that will likely get converted to "greasel" here within the next 2/3 months. I've already had the IP resealed, new fuel lines/injectors, main seals, water/fuel seperator, etc., within the last year or so, and really just need to hobble together a conversion kit DIY-style from the local ace hardware/home depot.
Provided that the fuel system is sufficiently purged before shutting the engine down, there is very little chance of damaging anything running wvo/svo, even on an older mechanically injected diesel like mine. Check out greasecar.com (sells conversion kits that cost about 3-4x more than DIY), many of the cars running those set up are mech.-injected veedubs. It is a good idea to strain your veggie oil well enough to remove as many little bits of crap floating around in the oil, though. Also, where you get your oil from/what kind of veggie oil you run will have an effect on the aroma of your vehicles' exhaust. Oil from Chinese/Asian restaurants are usually prized more highly than grease from fast-food chains due to the fact that these places generally fry with peanut and/or soybean oil instead of canola oil, and change their oil out more often than McNasties' and other fat-food establishments.
It's a good idea to poke around in your area and get an idea of how often places change out their grease and how they are currently disposing of their spent grease. Oftentimes, restaurants will give you their used grease for free, especially if they've been paying to have it removed. Be careful, though. There are some wierdos out there completely opposed to this "subversive" practice of energy independence, and you absolutely do not want the government to find out that you are no longer dependent upon the oil companies for fuel.