Blog-well.com has put together a great guide on how to transfer your site from WordPress.com (your url would look like this: yourwebsite.wordpress.com) to your own domain (yourwebsite.com) and fully hosted using your own hosting account.

Previously you ran the risk of losing your page rank and any search engine rankings and incoming link traffic, but the free report tells you how to take care of all that and move without cost in traffic or rankings:

Transfer Blog From WordPress.com to Your Own Domain

As an alternative, you can let a Ninja install your blog for free :)