-boRg-, I agree that nagging the admin to choose a non-default location and file name is probably the best line of defense. I wouldn't advocate an extension rename in place of your solution. But (you knew it was coming), if a hacker discovers the path and file name, a method of preventing the database from being downloaded is a reasonable second line of defense.
dpyers, I'm looking forward to your results. If there's something contained in one of your MDBs that causes a scripting error, perhaps something similar could be added to all our MDBs so that when they're renamed to .asp, a hacker is foiled. If some servers will attempt to send an unknown extension and not give the 404 error as mine do, your script error may be a better universal solution.