It can't I'm afraid mate. This forum script is really basic which is exactly why I used it. I wanted something basic and simple white so I could embed it in an inline frame in a "forum" page on the main site. So options are minimal, and in fact everything we can do is essentially already being done.
It isn't perfect and I'd quite like to setup a more advanced forum where lots of options like that would be available to us, but I'm reluctant to do that at the moment because we'd lose a lot of good threads on here. It's something I'll have to think about at some point in the future though because this is a bit disjointed and inflexible