Adding custom button/Link to post-new.php

Hi,
I want to develop a plugin that could show me some options on clicking a button while adding/editing a new post.Say like adding one more link in Upload/Insert. I dont know where to work into and i’m new to plugin development.please help me..
I went thru’ how to add new page to existing menus,but dont know how to add an element to an already existing page(post-new.php)

Thanks,
Prakash