It appears that some people are a bit confused about the difference between WordPress.com and WordPress.org. WordPress.org is the website that hosts the WordPress CMS development files and is where you can download the WordPress setup files to utilize the program on your own server. WordPress.com is also part of the overall WordPress organization, but is a place where you can sign up for a free account and use a copy of WordPress that is hosted by them. It’s works sort of like Livejournal or MySpace, but utilizes the WordPress engine. If you want to get a blog site up quickly and want to do a test of the WordPress system without having to do much work, it might be a good idea to sign up for an account at WordPress.com and try it out.
There are differences of course. You are much more limited when using a WordPress.com account than if you set up the program on your own server. They have a limited selection of approved plugins and themes–though the benefit is they usually just work and don’t require much if any set up. Unfortunately my plugins are not a part of their service (yet!). Also, they pay for allowing you to use their service by selling ads on your account site–money which you don’t get– and you aren’t allowed to add your own ads. Ultimately if you plan on really making any money you’ll want to transition to your own server set up.
If you don’t have webspace purchased yet and are still in the decision making stage, go get an account, it can’t hurt. It’ll get you an understanding of the basic workflow of posting.