change login page in Websphere Portal server 5.1

[sujith Acharya]

I am using Websphere Portal Server 5.1 for my application
I have following questions.
1.Suppose I need to introduce company logo as background image in login page, what approch I need to follow? Which all the changes need to be done in which files.

2. Can I change change the login.jsp in Login Portlet in installedApps of PortlaSever to introduce the image tag?

3.I read, we have option of loging in using login portlet or login screen. Whats the difference between them? and is it available in version 5.1

If i need to configure for login screen instaed of login portlet, what changes I need to make?

Thanks in advance,