THIS IS APPLICABLE TO UBUNTU 11.04
Normally when you are in a network you can log into basically 2 types of accounts which are local accounts and domain accounts. If you want to log into your domain account you have to click the 'other' category in the login window and enter your username.But this may be a bit annoying and there is a way to set visible your domain account name in your login window and even hide any local accounts.
This is the way.
log in to your domain account.Find the uid of you by typing id command in terminal.
uid=123456789(DOMAIN\username) gid=0(root) groups=0(root)
Here the UID is 123456789.
add the following line to /etc/passwd file.repalce UID with the number you have found in the previous step.
Hide local accounts from the login window.
edit /etc/gdm/custom.conf as follows.
Exclude=ALL THE LOCAL ACCOUNT NAMES WHICH SHOULD BE HIDDEN SEPARETED BY COMMAS.
Log out from the current session and see your domain account appearing in the login window.ENJOY!!!