How to access the outlook email compose message body.

hi,

I want to change the message body at runtime, I have created few email message template and a outlook ribbon for the email compose window. I want that when I select any template from the ribbon the message body inside the template should be populated on the open email message body, My problem is that I don't know how can I access the compose message body which is  already open, I can make a new email message at run time but this time I want to access the message body which is already open and replace the message body text with the template message text.

Please provide any link or idea, help needed...

Rohit