Really good primer on getting started with WVO here, with specific info on how to approach restaurants:
http://biodiesel.infopop.cc/eve/ubb.x/a/tpc/f/159605551/m/347104314
Turbo6bar is right... be chosey about oil. There are plenty of restaurants out there, so take the time to find a reliable source of consistent fuel. For whatever reason, chinese resaurants seem to have very clean oil.
I'd probably avoid greasel... there have been some unhappy customers posting on the
forum I participate in. Some questionable claims, and the post-sale support seems to be spotty.
Biofuels sells very high-quality stuff, and offer fantastic support.
Really though, if you're halfway handy you can set up a really good, reliable system.