Just install the Crystal Reports Viewer.... It allows them to view the reports. But they'll have no way to modify them.... And they wont need to Connect to the database to refresh and grab new data/new parameters. (in other words they wont need a password to connect, it will pull data from the database without it.)
Or, do what Lockwelle suggested and make it read only. Although, i think even as read only they could save it as a different name, then go back and rename the one they created and end up saving over the one you created. so.... still leaves you volnerable (if my assumption is correct, i'm not totally positive about that).