Worpress Sign Up Page and Multisite


I'm running an installation with a Premium Theme that includes a slider on the home page. When new users sign up to create a site the sign up form appears just under my slider and full page which is quite absolutely not the place. I want to control where the sign up form appear and it should be in a separate page that I will call sign up. This is already the case for sites like edublogs: http://edublogs.org/signup/

I thought that it was quite obvious but in fact this is the first thing I need to do before customizing the sign up page.
In the home page there will be a whole marketing presentation and call to action button to encourage people to register for free in our site. Second I would like to customize the page to make the process a bit more sophisticated than simply adding a username and password. They should also be able to choose the domain name domain.mysite.com just like edublogs or wordpress.com.

Appreciate your help!