Rebecca, I remember a previous post that a visitor found storage at the bus station, so I called to see if still available, and it is. Lockers are $3 for the first hour and $1 per hour after that. It's difficult to find storage short term because of security/liability, esp. since 9/11. If you are staying at a hotel, they will often keep your luggage for you short term.
The storage lockers were a “pilot,” the kind of small test that city government frequently uses to test a new or controversial idea. The city offered up the lockers for individuals to use for months-long stretches. At the time, city officials warned that “misuse of the lockers, vandalism, or other unanticipated results,” could force them to cancel the project.