To edit your message, you have to be logged in properly. Then you'll see an icon in your message for editing it.
As for posting images, I haven't done it myself, but I believe you have to upload the image to a website, such as geocities or something, and then you link to that website. A fellow zx6r.com member generously donated some webspace for this purpose (as long as it's not a link for your signature):
/forum/topic.asp?TOPIC_ID=2521