Col,
Do you have your own hosting? If you do, you can edit these two files:
functions.php (you can create this file if it doesnt exist)
sidebar.php
To learn how to "widgetize" a theme, check out this link:
How to Widgetize non-widget Wordpress theme
If you are using the wordpressdirect hosting, Im not too sure if you can do it. Dont quote me on that though, because I havent tried. I am using my own hosting.