Currently, there are two places you can upload your work. The first is right here.
http://mtm2.com/~tracks/In the upper right corner is a button that'll take you to the upload page. Just fill in the track name, your name (nick name is plenty good), indicate what kind of track it is, and of course include your track - which must be zipped up. Click upload and be patient while it goes. When it's done, it should be listed on the download page. If you have problems, let me know.
The second is kc's place.
http://vales.com/mtm2/You'll see the menus on the top of the page. Goto tracks>upload and the procedure is much the same. He's got a few additional instructions there for you, and you can optionally upload a picture. The track will not appear on the active download page immediately, it will be tested first, but that doesn't usually take very long.
We're looking forward to what you've come up with.