I'm not 100% certain of this, as I've not gotten the chance to test it yet, BUT if your question hasn't been answered, I believe that for custom campaigns to appear in the menus they need to be manually entered into a campaign manifest (text file) somewhere in the game directory. They'll probably change this with the release of the SDK to be more user friendly. In the meantime, as long as your map files are in the Left 4 Dead maps folder, you should be able to open up the console (the tilde key, ~) from the main menu and type "map mapname" without quotes; for example, "map l4d_hospital01_apartments"

As for the map editor, the actual L4D SDK (Software Development Kit) hasn't been released yet, but if you have any orange box games (HL2 Ep2, Portal, TF2), there are tutorials for setting up the existing SDK to work with l4d.

Of course, I'm a little late on the uptake, but hopefully SOMEONE will find this useful