I run my VW Golf on 100% biodiesel almost all the time. As Banana said, diesel engines require no modification to run on BD. There is one exception to this and it's not really a modifcation - cars that have older hoses or have run on dino diesel for a while will need to have those hoses replaced and a fuel filter change or two. BD is a very good solvent and it will disolve older rubber hoses and the crud that builds up from prolonged dino use.
BD has a higher gel point than regular diesel, so in the winter, depending on climate, you my need to use a regular diesel/biodiesel mix. During the winter, I switched to running B20 to deal with the freezing thing. You don't need a second tank or warmer or anything.
Are you planning on brewing your own or are you looking to hook up with a coop or something? I'm a member of a coop where we brew BD once a week. I've learned a lot about the process - so much that I wouldn't do it myself without investing in a bunch of equipment.
I don't run on straight vegetable oil (SVO) or waste veggie oil (WVO) as both of those require modifications. I think a popular one is called the Elsbit modication. Have a look at
www.biofuels.coop and you may find some more links to help you along. Let me know if you've got any other questions. (This post was entirely typed on my iPhone's keyboard so please excuse any typos.
)
Oh and diesel engines don't use spark plugs! Compression combustion FTW!!! You should also check the forums at tdiclub.com - they have a biodiesel forum.