Where to start?

I saw the sidebar to bikesdirect.com, but i'm not sure whats a good fixie. My friend owns the hour with upgraded parts but I'm not sure should i start out with buying parts or buying a fully assembled bike. I'm looking to spend at least 600 dollars. Any recommendations on wheels, frame, gears, and etc?

or a fully assembled bike?

What exactly is gear ratio? What is a good gear ratio?