yep, I concur with everyone else. Use mineral oil, never any kind of vegetable oil. Pour it on and rub it around until it won't take anymore, let it sit for a little while and then wipe off the excess. Once a day for a week; once a week for a month; and there-after, once a month or whenever it looks dry. Always wash with hot soapy water and never ever put it in the dishwasher.
Another advantage of wood cutting boards over plastic is that they say the wood acts as a natural anti-biotic, so the stuff that does soak into it is naturally taken care of, where-as with plastic (which is porous btw) the stuff that soaks in, and gets trapped in all those little cuts can thrive and grow into some nasty bacteria.