theres two methods..

if its a pic on your hard drive.. just press the upload pic button when you make your post..

if its already on the net.. (or you were one of those people who go upload a pic in Area51 then link to it from there.. which is kinda stupid cos if we need more disk space at anytime.. we will delete uploaded pics..and because when we move to the new forums software chances are we wont bring over the uploaded pics).. then you use (img)http://url.to.your/pic.jpg(/img) and replace the ( and ) with [ and ].