Hi welcome to the world of WordPress. 🙂
My answer is a bit indirect…
I think before you even start thinking about creating a theme, you should really understand how to create content in WordPress through writing blog posts, pages, how to edit the navigation bar, how to activate themes/plugins, and how to use the settings like the permalinks. A great site to learn all this stuff relatively cheap are the video tutorials WP101.com.
Before you can really start creating a them you’ll want to know what it takes to make a good theme and the only way to do that is to use a WordPress for what it was meant for: to create and publish content.
When you’re ready to create a theme, I’ve heard the following free WordPress framework packages make a great start: Thematic, Theme Hybrid, and Carrington.
Good luck and great to have you on board!