If you have Patched to 2.4!!
This Guide will show you how to patch down from 2.4 to 2.3.3
Note: You will be deleting files!
First, Go into your World of Warcraft folder and find the Data Folder.
Next, Delete any files with the name patch in it (like patch.MPQ or patch-2.MPQ)
Now, Once those are deleted, Go back to your main World of Warcraft Folder, Find the program Repair and run it. Repair will patch you back down to 2.0.0. Once Repair is finished, Patch Back up to 2.3.3.
Warning!: Repair will take a while!
If you don't have the original patches in your World of Warcraft folder, Go to World of Warcraft Official Patches Demo, World of Warcraft Official Patches Mods - FileFront.com and download the patches you need and install them.
Now, if you want to prevent from downloading Patch 2.4 again...
Go to your WoW Folder and change your realmlist back to the private server(it will change when you patch up), save it and then find WoW.Exe, run it and it will get past the Launcher.
thanx to maven