That would be done in your theme.
ok I just modified the 2010 theme do you know where that is in the code?
There should be a file in the theme called categories.php. In there, it calls the sidebar. You can try removing that.
(Can a mod move this to Themes support? That’s really what it is, I think.)
Quick question – how do I know if a theme lets me do this with my categories? Like, what code word am I looking for, or is it just a bunch of trial and error?