I swear I read this somewhere in the community that to change styles you need a certain styles exstension, which I can't find nor can I find any other referance to it...
Well I've come to the conclusion that there is such an exstension. But I can't find it under manage exstensions. Actually under manage exstensions I just get 10 or so Whisper Exstensions.
Unless I'm misunderstanding your question then there's not actually a styles extension. You can change the styles under account and then change stylesheet.
If it's for your own board and you want to add them then go to settings and style management.
As for the 10 whisper extensions.. sounds like you have a problem there. I've heard of it before but can't remember the resolution to fix it. Someone else here will be able to help you more for sure.
giginger: His problem, from the sound of it, is that he's using PHP5 and hasn't fixed the bug in the extension manager. The same thing happened to me and the link I gave describes the error and tells how to fix it.