That would give you a year's worth of mortgage payments at last year's fixed rate. Whether you choose an ARM or a fixed rate, lock it up. A traditional rate lock is a lender's guarantee that you'll get a certain interest rate, number of points, and other cost-related features. Here are some rate lock pointers. Whatever lock you choose, get it in guarantee in writing.
Oral agreements are difficult to prove.
Unless your contract says otherwise, a rate lock could prevent you from taking advantage of lower rates, but it's not likely they will drop. Lock in as many of the costs you can, the rate as well as points. In this market, that would almost guarantee you a higher rate. Shop around for both the terms of the lock contract and its cost. Others might charge the fee at settlement.