CrustyFN - It's true that you can upload an attachment only once and you can't use the TFL URL of an attachment to upload in a new post. But, all is not lost. In the same manner you got the URL of the attachment, copy only the "attachmentid" number (usually a 5 digit number). In your new post paste that number between "attach" tags. That way you can use the same attachment in several different posts.
The "attach" tags will look like the following:
and will produce a link to your image like this:
Or you can use the complete URL of the attachment and paste it between img tags to have the picture show up immediately (as Capt Charlie said above, it must be the complete URL from "http" to the end):
The tag/URL will look like this:
and will produce this:
Thanks to IM_Lugger for the use of his image. It was the first one I ran across.