Let's stick this topic up.
Here's how to do it: (If you logged in to the archive then avoid step 1)
1) Register, filling your details as you go along.
2) Log in unless you registered.
3) At the bottom of the "Level packs" page click the button "Upload a level pack"
4) Choose a name for your pack in the "pack name" box.
5) Describe the pack (If you want to, it's only optional)
6) Find the Common path for the level pack. In other words click "Browse" and find the level pack in your file.
7) Click "create" and there you have it! Your level pack is there at the top of the first page.
It should be noted that you can also remove packs and edit them.
Yes, I know that, but it's more important to get the levelpacks up. That's the first thing to do after all. At least you'll let the others have a stab at your levels and see which ones go wrong.

Don't worry too much about the editing and removing, the buttons are there when they sign in and move to their level packs.
Un-stickying this because nobody uploads new NL/Lix levels to Mindless's database.
-- Simon