Alter the way messages are displayed on a web page

I have a custom build website, in this is a message inbox, at the moment it displays a list of conversations with other members in one column. I would now like for the left column only to display new messages and for the messages which have been replied to in the right-hand column, where each message has a 'Delete' button, I would now like a check box with a 'Delete selected' link at the top of the page. New/Unread messages should also have a different background color to replied messages. I also have a small problem with users reopening a deleted message string, again not a huge job.