In order to connect to Noxious-WoW, you will need an account (which you can get by registering), and a Wrath of the Lich King client, and all of our custom patches.
This can be found in the Downloads link.

If you already have your own Wrath of the Lich King client, you will need to delete all the custom (non-Noxious) patches and apply our patches instead.
Please note: having multiple patches (even if named differently) can collide the two patches and create an unstable experience, and possibly even cause you to crash. We highly recommend you not to use any non-blizzlike patches in addition to Noxious-provided patches.

This is how the "Data" folder should look like, without any custom patch in it: 

On top of that, you will need our own patches (which you can get from here).

Open up your WoW directory, and go to the "Data" folder. From there, continue onto "enUS" (or whatever language you have), and find the file: "realmlist.wtf".
Open it with a notepad or any text editing software.
Delete whatever it says there, and replace it with:

set realmlist logon.noxiouswow.com

Hit save and close the editor.

This is what your "enUS" folder should look like by default: 

Don't forget to read all about us, our "Welcome to Noxious-WoW" page, our special boxes, and the VIP page in case you're interested in some cool perks.

You can now log into Noxious-WoW!