Make sure you are logged into the gallery, as it is a separate login. Once you click Add Media, enter any titles or tags you want, then drag and drop the picture file onto the box that says "Drop Files Here to Upload". That's really all there is to it. It takes maybe ten minutes for it to show up in the gallery. How do you mean it is posting as "unavailable?" Is it an error in the Trainz Gallery? To post in the forums, click on the "Full image", right-click and select copy image link, then use the insert picture icon that looks like an image to post.