MonitorES pauses media playback, adjusts IM status when your PC is locked
The utility also lets you automatically update your instant messenger status, mute your system, and pause playback of 16 different media players including Winamp, Foobar, and Windows Media Player. As for IM clients, MonitorES supports Google Talk, Yahoo! Messenger, Digsby, and Miranda.
When you login to your computer again, media playback will resume, your IM status will be updated, and of course your screen will turn back on.