Create a blog entry. Look in the box on the left hand side with your username in it. There's an item labelled "create content". Look in there and you'll see the types of things you can add to the site. Either a blog entry or a page is appropriate.

Give the item a title and description. You should see a tab for attaching a file. Use this to add your .zip. Make sure to read the instructions-- you need to choose the file, click attach, and then submit the blog entry.

In the pulldown menus for the various tags, make sure it has the tags "community" and "soundtrack" as well as whichever game is appropriate.

Then send me a private message alerting me to the post.