Own subdomains for users (how to make it in htaccess)

I realy need to give possibility to my users have their OWN subdomain on my Drupal site.
Means:

Any user, who type:
http://My-user-name.example.com

will see standard profile page (but they are still on the same subdomain URL, there is NO redirect):
http:// www.example.com/user/My-user-name

I know it is possible to do by htaccess and mod rewrite, but I try many test and no luck :(
Any glue? Thank you for your help!