Your upload worked just fine. All you need to do is copy the URL displayed below the image when the upload is completed and then paste it in the "Optional Image URL" box at the bottom of the page on the Message Posting page.

The URL should look like this:

http://www.chipguide.com/chimage.php?image=/IMG_1631.JPG

To get fancy and do multiple images is a bit more difficult - read the "Formatting" section by clicking on the "Formatting " button in the Yellow band above.