How to customize discussion board in Sharepoint 2010 by editing thread.xsl

Hi,

I need to customize discussion board of SP 2010.

Because I need to provide the option for Edit and Delete in Discussion board Replies

1. User–who has initiated the discussion should have facility to Delete any reply for his discussion
2.  User-who replied to the discussion should have facility to Delete/Edit only his/her reply for that discussion.

kindly help me in this to achieve the goal.