Looks like you have already figured it out when I viewed your site.
What do you think that means? It means give the sidebar a HUGE margin on the right, but that's not how to do it.
It's not easy. It's much easier to either try a theme with the sidebar on the left and then change it to match your needs or copy their "structure" code from their
In CSS, you can't just move or position one thing and expect everything else to shuffle around. You have to change everything.
You have to adjust the following:
sidebar (or menu)
If you are using Firefox with the Web Developer Add on (get it now if not!), choose OUTLINE > BLOCK LEVEL ITEMS and you will suddenly see boxes all around the different "containers" on your page. You got to "move those lines".
Look for content that is near to the top of one of the lines that you want to move and then view the source (View Source) and find that content. Look for an ID or CLASS and that is your style reference to look up in your
style.css that needs changing.
Here are some more resources:
Finding Your CSS Styles
Codex - CSS Fixing Browser Bugs
Codex - CSS Troubleshooting
Position is Everything's 3 Complex Column - Perched on a Lily Pad
Position is Everything Piefecta Rigid 3-Column Layout
WordPress Design Sandbox Article
Working On CSS and the WordPress Theme (using a sandbox)