categories as pages

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?

See if a review of these helps with that question:
Stepping Into Template Tags
Stepping Into Templates
Template Hierarchy
Theme Development