If you already have the client and are just wanting to connect to your server, you generally don't need to patch WoW.exe (or whatever it's been renamed to) in order to update the realmlist file.
There are several great instructions around this forum to find out how to set the correct IP in your realmlist (as well as patching the executable, if you are still so inclined). I'd suggest starting in the 'Tutorials' sub-forum. ;D