Cannot figure out how to automatically have button value put into textbox.

Hello All! I'm trying to get the button value to be automatically put into a textbox. The username is the button and when another user wants to send that user a message, he or she clicks the button prompting them to the send message page to which the "TO:" textbox is already filled with that user name?

It's not working!

this is what I have:

button:

<input type="submit" onClick="document.location.href='http://revideolution.com/senduser.php'" name="tousercommunity" value="conrad" />

textbox:

<label>To:<input type="text" id="tousercommunity" value="<?php print($_SESSION['tousercommunity']); ?>" />