I may be able to get my hands on a oaken barrel that I'd love to age a Scottish ale in. What can I do to sanitize it adequately and minimize oxygen exposure?
More beer has a great guide on taking care of oak barrels which covers cleaning, sanitizing, etc.
The overview is: keep it filled so that it doesn't dry out and use a sulfur-dioxide mixture to sanitize. The oak will soak up some of the beer over time, so brew a little extra and keep it on hand to refill as the level goes down.
You should also remember that oak has some oxygen permeability which is one of the features of using an oak barrel.