I have told you more than once now and in more than one thread that you cannot create a custom log-in on a free hosted WordPress.com blog. You cannot become a mini-wordpress.com in your own right on a free hosted WordPress.com blog.
Go to Create A Network http://codex.wordpress.org/Create_A_Network
WordPress.com and WordPress.org are completely separate and have separate logins. If you don't have a username account at WordPress.ORG click http://wordpress.org/support/ and register one on the top right hand corner of the page that opens, so you can post to the support forums there and receive advice from WordPress.ORG bloggers.