You cant post attachments right now
You'll have to get an account on a Photohosting site.
http://photobucket.com
http://imageshack.us
http://zoto.com
Then you choose the link that looks like this on Photobucket and I think Image shack
(similar to that)
and on Zoto you use the links button and click the other one thats NOT HTML!
Hope that helped and Welcome to PT!