All you need to do is find a host for your image, then stick the web address of the image between two image tags. If you check out the new post screen, you'll see a
http://static.lfnetwork.com/lucasforums.com/images/editor/insertimage.gif). Click on that and it'll create the code for you.
If you don't have a host for your image, you can use ImageShack (link (
http://www.imageshack.us/)). Just click the browse button, choose an appropriate size, then click the Host it! button. Wait a few seconds and you'll be given a bunch of codes. The bottom one is the direct web address to your image, while the rest speak for themselves.