Forum A little cosmetics
 

I've recently started spreading my new forum around, but I'm having some issues with what you might call cosmetics. Facebook is a prime example:
Whenever I post a link, you get this little box for it, where it says
"Forum name" - The front page
"url"
vBulletin 4.0 Publishing Suite with CMS

And of course I don't have much in the way of images yet, so I don't get any nice thumbnails to choose from. I'm just wondering where you'd go to change this aspect of the appearance? As always, I'm just as happy for a direction to a section of the manual that I've overlooked as a complete description here.
Thanks in advance!