First, in your World of Warcraft folder, which is usually located in C:\Program Files\World of Warcraft - find your "realmlist.wtf file" - open it as a notepad/wordpad
it should have the following
US Players
set realmlist us.logon.worldofwarcraft.com
set patchlist us.version.worldofwarcraft.com

EU Players
set realmlist eu.logon.worldofwarcraft.com
set patchlist eu.version.worldofwarcraft.com

What you do is modify that file, simply change the original into this:
US Players
#set realmlist us.logon.worldofwarcraft.com
#set patchlist us.version.worldofwarcraft.com
set realmlist myserversucks.zapto.org

EU Players
#set realmlist eu.logon.worldofwarcraft.com
#set patchlist eu.version.worldofwarcraft.com
set realmlist myserverblowsadick.zapto.org

The "#" tells the notepad or wordpad not to include this line, it is commonly used for players that play both retail and private servers, because now to switch back and forth, all they need to do is remove the "#"'s and the "set realmlist wowforever.zapto.org" - and your back on retail.

Anyway, after you have changed your "realmlist.wtf" file, go to:
http://www.omgwow.com
to create your account.

Once you have done these simple steps, your all set.

Make sure you have World of Warcraft: The Burning Crusade (not need but recommended, look below for a free download)
and all the right patches.

Latest Patch - 2.4.3

Server Patch - I forgot maybe 2.3? ah just try it i guesse

Free Burning Crusade Download:
[url]
http://www.exodus-server.org/upload/patches/tbc/WoW-BurningCrusade-enUS.exe
[/url]
World of Warcraft Patch Downloads:
http://worldofwarcraft.filefront.com/files/World_of_Warcraft/Official_Releases/Pathces;5994

Made by Caleb

I just copy and pasted exactly from caleb's post before forums go wiped