I'm afraid you cannot use OptimizePress on free WordPress.com blogs. WordPress.com is the free hosted blog service from WordPress, but this does not support the installation of external premium themes like OptimizePress.
You need to actually have your own web hosting and not use the WordPress.com WordPress service - as you will see on our sales page, you need to use the WordPress.org script on your own hosting. The script itself is free but it must be on your own hosting as the wordpress.com free blog service does not allow you to install themes.
I recommend following the tutorials in the members area on how to setup your hosting and domain if you're not sure how to do this first - then follow in the install tutorials for setting up wordpress on your site.
We recommend Hostgator if you have not yet chosen a web host -