iTunes lacks two things when you want to use it to DJ: the ability to preview the songs, and a way to prevent changing song by mistake when selecting a song to add to the playlist. There is a way to solve both problems.
Log onto your Mac on your regular account; the one you'll use to prepare your playlist. Open iTunes and create a new playlist for the party. Put some songs in it. Share your iTunes playlist. Log on as another user and open iTunes. Select the shared playlist from the first account and play it. Switch to the first user. The Mac keeps playing the songs from the second account. You can now update you playlist without having to fear a mistake when selecting song while the second account is playing it.
To be able to preview the songs, you need two soundcards (I use a Tascam US 122 USB external interface). Simply choose a different sound card in the System Preferences for each account. VoilĂ !
Mac OS X Hints
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