To post an image do the following, quite easy really :p.
put the [img] tag infront of your file url, and end it with [/img]....so you should get
[img]http://www.insertyourpicturehere.co.uk[/img ]
(dont put the space in on end tag like I have, its just for show so it doesnt think there is a picture which doesn't exist and show blank space!)
Do this and your picture will show on your post. Remember some forums are slightly different and need [IMG] in caps to work others just lower case.