To insert an image I suggest looking at Feareh's tutorial:
http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=38448.0 (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=38448.0)
It is similar to just posting an imaging in Post reply. Good luck!
(You can also take a look around the tutorial section in Miscellaneous. There are some more tutorials about this)
You are using the attachment button. ^^
Just upload the picture from either Tinypic or Photobucket and put the picture's url in this: (DON'T put periods)
[.img](URLHERE)[./img]