Charlie, first you need to resize them. A good picture for this place or TF is 800 by 600. If you do not have any photo editing software, or its a pain in the ass, go here:
http://www.picnik.com/ Its pretty straight forward and simple to follow.
Now you have two choices.. Find a "Host" for your pictures. Once you do that, right click your mouse over the picture, copy and paste the Location of the picture.
In the text of your message, do this
Paste your location in between the and your done.
OR you can use CBAngler as the host, using additional options, attach files, Manage extensions.