Go Admin->Site Building->Block.
Click on "Configure" link right to "User login" Block.
Go to "Page specific visibility settings", check the radio button "Show on every page except the listed pages."
And specify the pages where you do not want to see the login Block.
You can also able to specify "Role specific visibility settings" for this block.
Comments
Configure 'User login' block
Go Admin->Site Building->Block.
Click on "Configure" link right to "User login" Block.
Go to "Page specific visibility settings", check the radio button "Show on every page except the listed pages."
And specify the pages where you do not want to see the login Block.
You can also able to specify "Role specific visibility settings" for this block.
Hope this will help,