Change layout of child page

Hi all,
I have created a 3-column wordpress theme using Artisteer software.
I am interested in keeping the 3 columns (1 Posts column and 2 sidebars) as is on my main page but I need to have some other pages on the site only with 2 columns (1 Posts and 1 sidebar). Questions:
1) Any tips on how to set this up?
2) How do I change the content in the sidebar on the pages with only 2 columns so that differ from the sidebar on the main page?

Cheers /John