Default Domain - Intranet

I have added my default domain on my IIS 6.0 server for our Intranet. But,
when users try accessing the intranet, the userid and password box appears,
and when they type in their username and password and submit, by default the
"intranet.xyz.com" appears as follows:

intranet.xyz.com\username

So, they will have to manually go and delete the "intranet.xyz.com" and
enter the domain name, and then they can get it. Not, sure whether there is
a setting on the browser side that could be affecting this.

thanks in advance