Confusing about login name in AD-proxy authentication?

["chowalit.lab Chowalit Lab Linux" <chowalit.lab@xxxxxxxxx>]

Dear All
      First of all I will explain about my system.
      I have authenticate proxy with account from windows 2003 server.
I use ntlm.
      On login pop-up, I must use "MYDOMAIN\username"  into login box.
     My question is --> How to configurate my system (both of windows
and squid) to support login name like "username@MYDOMAIN"?

Thanks you
Chong