Try looking at the options under Style Manager > pick style > StyleVars. There are a couple of options there to try.
Also, to find the template to modify, do this - vboptions > General Settings > Add Template Name in HTML Comments > set to Yes . Then go back to your page and view the source code and you will see the name of the template called around your part of the code.
That was it! "Message Area Width". Thank you!! (thank you both for your replies)
Now I just need to find where the setting is so I can shift it so it's aligned center (it still has about a 50px gap of unused space on the left hand side, squishing my smilies on the right)