Disable login password for shared computer with multiple users?

Hi,

I'm setting up a new computer for my parents. To enable them to have their own bookmarks, playlists, music library, calendars etc I have set them up with a user each. What I would like is for them to just be able to click the relevant user on bootup and automatically login but still be prompted for their password when installing apps. Both users are admins. Is this possible? Is there a third party program or script which could enable this?

The only alternatives seem to be auto login to one user and switching to the other or my parents sharing an account.

Ryan