DJ Use
Here's screenshot of a "DJ" setup (it's from MC13, but MC12 is almost the same.)
[url=http://i224.photobucket.com/albums/dd212/AB2K/MC/MC_DJ.png][img]http://i224.photobucket.com/albums/dd212/AB2K/MC/MC_DJ_tn.jpg[/img] [i][u]Click to enlarge.[/u][/i][/url]
The first MC instance is on the left. It is set to use a zone that outputs to headphones. The split view option is set to two splits. The top split shows the library and Playing now is in the bottom split. I can drag files from the top split to Playing Now for previewing them. I can also double-click a file to do the same because I have set the "jump on play" option to none and double-click to add to Playing Now instead of directly playing the track. I have added the Playing Now and Zones buttons to the top toolbar, though I don't need to use them with this setup. I have hid the tree by double-clicking the divider.
The second MC instance on the right is set to use a zone that outputs to speakers. I add tracks to its Playing Now list by dragging them from the first MC instance. In addition to playing audio I can detach the display and show a visualization on a TV or projector that is connected as a secondary display.
This setup works fine with the common 1280x1024 display resolution. I selected the Z skin because it allows a quite narrow MC window (the minimum width varies from skin to another).
Thanks to Alex B for the above instructions, originally posted in this post on Interact.