Mario. Congrats! This this the type with the wraparound and the tummy cut? I hear they are muy toneful!
To put a pic up, first off, get it somewhere up on the web. I use a variety of place, most notably Photobucket.com, since it's free and easy.
Then when you hit the 'Reply' button here, you'll see a series of gray buttons at the top, above the text box. Punch the IMG button and a box will pop up with a place to put the URL of the picture. I usually have two copies of my browser open when I do this. Then get the URL from Photobucket (it'll be the first little box below the thumbnail of the pic. Select it and copy it.)
Then go back to your reply here and paste the URL into the popup box space, hit "OK" or whatever it says, and you're done.
If you stash the picture elsewhere on the web, the second part of that process may be a bit different. While the reply box and IMG button popup box are open here, open another copy of your browser and go to where the picture is. Open it and then RIGHT click on it. From the popdown menu, select properties. There should be a URL in the box that pops open. Copy that and then come back here and paste it into the IMG URL popup box.
On a Mac, I believe when you have the picture open, there's a menu option someplace to select Properties from, in lieu of a right-click.