One of the coolest things with OSX Lion is the ability to use the iTunes artwork as a screensaver. And when you do that, you can actually play the music that belongs to those albums without exiting from the screensaver.
Make the songs in your iTunes should of course have their album cover artwork. The second thing you have to do is to make sure that your screensaver requires you to enter a password before it exits and reverts back to your regular screen. To set a password, launch System Preferences, open the Security & Privacy preference pane and select the General Tab. Mark the box that says require password after sleep or screen saver begins.
To setup your screensaver, open the Desktop and Screensaver pane from System Preferences. Select the Screensaver tab. Under the screensavers selection, drop down the Apple arrow and select iTunes artwork. Click on options to select how many album covers to show at one time and the time delay before it flips to a new set of artwork.
Once the screensaver activates, hover the cursor to an album cover. A play symbol will pop up. Click that to start playing songs from that album. You can use the music function keys on the keyboard to move through songs, but only if there is a password requirement.
Your Mac will be even more YOUR Mac when you use iTunes artwork as a screensaver.