Hi Chris, on WordPress.com, some design and layout changes are possible with the Custom Design upgrade.
This forum is actually for folks running WordPress on their own hosting, not WordPress.com. :-)
For help with WordPress.com sites, feel free to post in the forums here: http://en.forums.wordpress.com/
The CSS Customization forum is especially for questions around using custom CSS:
http://en.forums.wordpress.com/forum/css-customization
Here are some tips on getting help in the WordPress.com forums: http://en.support.wordpress.com/getting-help-in-the-forums/