david

Well first of all I think you copied the wrong link. I would go straight to the file's webpage and copy the URL just to make sure, since your link brings me to the Mediafire homepage, meaning you probably accidentally copied a link to your control panel rather than the actual file (don't worry, I've done it before).

Second, all you need to do is paste the link into the topic. Just make the topic, explain your rig, add some pictures of it, then add the download link last (at least that's the standard format. Of course you can switch it up a bit). Some people even add an image saying "Download" then add a hyperlink to the image leading to the Mediafire download. However you wish to put the link into the topic is up to you.