I want to change the sign-up page - how can i do that?

Hello,
I have a multi-wordpress and i want to let people sign-in and build there own wordpress.

I understand that the way to do that is by going to this page:
http://bestpages.co.il/wp-signup.php

but is there a way to make it look better? is there a plugin that can help with that? or is it just hard code thing of the wp-sugnup.php ?

thanks
Nir