Displaying Block content

Hi all,
i just want to redesign the the "block visibility in pages settings" from the text area to check boxes having the node titles. User can check or uncheck the nodes they want to display the block content. It is working fine for me except showing the checked check boxes. I need to display the pre-selected check box in block configuration page. ( ie; problem with default value in checkboxes)

Thanks in advance.. Any reply..