OK....now I'm in another post own post trying to do an attachment.
And now I'm pointing to the attachment from an HTML IMG tag.
<img src="http://www.cellar.org/attachment.php?s=&postid=4914">
The trick seems to be that you have to *post* the message, even though the attachment is uploded if you push the preview button nothing happens to it. The path to the file has to be in the attacment field at the time you press the post button, and I think it clears out if you only preview.
Let me try that "IMG" button again:
Yeah, see: you only get a link. Whatever. :-) And now I'm getting an attachment dialog on the edit page..."Keep current"/"Delete current"/"Upload new". Could have sworn that wasn't there when editing a post that didn't have an attachment the first time.