below the text box, you obviusly can see additional options
, to the right of it, you have the Imageshack toolbar
, you simply browse
for the picture and click Host it
once the picture is uploaded-hosted, you copy-paste a link, from the new window that poped out. the best choice would be thumbnail for forums
, either 1 or 2, if the first one doesn't work, you try the second one
i think your problem was that you closed the pop-up window.
i may have complicated a bit, but i hope it helps.