This is a guess, I would check it out but atm I don't have access to my ftp server.

in /templates/default/main.tpl there should be something like a <div class= latest posting> try copying that to make a new div with just the image in it?

If it's not in main.tpl it might be in index.tpl in .../subtemplates .

I would check it out on mine but I can't so don't blame me if it goes wrong.