1st upload your image to something like ImageShack, then once you have uploaded it there, copy and paste the direct link that it gives you between the "img" tags.
Or else upload it as an attachment - look below the text box where you type your replies and you'll see a section called, "Add an Attachment". Upload the file and hit submit, it'll come up on your message.
Kati
In hibernation but half awake - will stick my nose in every so often!