Dude I have tried everything for about three hours, I want to join the Arelith servers and I firmly believe im following every instruction to the 'T' and it continues to let me make my character but when I hit play it kicks me to the main menu and says 'Authentication key denied'.

Which game are you talking about? NWN1 or NWN2.

For NWN1, did you install and run "premium modules re-installer" ?

NWN1 and yes I installed the premium module multiple times unless I somehow did that wrong.

I need cd-key for multiplayer game

Then you need to go here http://www.gog.com/en/support/contact/technical_issues_with_games/neverwinter_nights_diamond_edition

Where it says problem type, choose multiplayer key request.

I need a set of new Cd keys for nwn diamond please

I need a CDKey for multiplayer gaming!

This forum is not where you ask for a multiplayer key.

Then you need to go here http://www.gog.com/en/support/contact/technical_issues_with_games/neverwinter_nights_diamond_edition

Where it says problem type, choose multiplayer key request.

The changelog today said it got a cdkey replacer. How does that work?

I haven't redownloaded to see, but I imagine it is just like the NWN2 cdkey replacer, in that you click on the .exe and copy and paste your keys in there, instead of directly into your nwncdkey.ini

There doesn't seem to be anything new really. Just a section in the library with some keys. Where in the exe should I use them?

In NWN2, the CDKey Replacer is called SerialTool.exe.
Do you have that?
If so click on it and a box will open with the default keys in it.
Copy and paste your unique keys from your library into the three boxes, then click on save and close.

Or you can just open nwncdkey.ini & replace the 3 default keys there with the ones in your library.