First locate the directory in which the picture your wanting to insert is located in. The get a free image hosting site www.iownjoo.com is the best. Look on the left of the screen, it will say free image hosting. Click there and you will be taken to another screen. Click the browse button and find the image, after you see the path in the text bar hit enter. You will be taken to a new window, it should say your image was hosted at blah blah blah. Next highlight that URL, then right click, then click "copy". Next go into the thread you wish to put a pic, in the text bar right click and click paste. The url should pop up. Next look at the beggining at end, it should have [URL]blah blah [/URL]. See the tags that have url in them? Change them to this [IMG] blah blah blah [/IMG]. Make sure not to have spaces between the tags and the URL itself or it wont work.
Also this has nothing to do with Diablo II so its moved to the help.