When I choose "What stylesheet do you want to use for this forum?" in the admin page it reverts back to the "default" style sheet even though I selected a different one, is this a bug? Where do I edit this manually?

Check your permissions on your theme.inc.php file...

I changed the permissions to 777 and still no worky.

If you change it in the theme that will only apply to new users and unregistered users.<br /><br />Registered users (including yourself) need to adjust this under display preferences under "my home".<br /><br />See this document for more help.<br /><br />

Josh<br />Is there a way so that I can have one of my forums a different background color? For all users, reg and unreg?<br />Maybe put the color code in the header? I dunno

Answered in more detail here.