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.