Setting up new blog customers

Hey,

Ok, so I have Blog Templates setup on my domain getcrazynation.com. I have also installed Pro Sites and I understand how it works to get current users to upgrade. But, how would I go about setting up a page on my live site getcrazynation.com for a new user to sign up for a new site and choose which package or level they want. Is there also a way for them to choose their subdomain ex. my site.getcrazynation.com?

Thanks
Chris