My htaccess Problem

hi friends,
i have faced a problem relating to htaccess and can't getting it solved.
i need to redirect only one of my webpage.
http://www.sitename.com/myaccount.php is to be redirect ---> http://www.sitename.com/username
it means when the user type the second url in the address bar, it will redirect to his myaccount if his username exists or otherwise in login.

if anybody help me regarding this i will be highly obliged

pranoy

Something like that is a start, you need to explain more what you need.. like what they type, what they are actually viewing, and what shows up in their browsers address bar..