You can only borrow points backwards one use year. You also, according to the current disney policy, can only borrow what you need to make a reservation. In other words, unlike banking you can't just call up and say "put my 2010 points in my 2009 use year." As a practical matter, though, you could accomplish this if you really wanted to (not sure why you would). You could just call today and make a reservation that requires you to borrow all of your 2010 points and then cancel it. Now all your 2010 points are in this use year, since borrowing is a final transaction.
As a practical matter, you really only have access to two years ahead. If you call to make a 2010 reservation (assuming you're in your relevant time window to make it) you can borrow 2011 points.