Network Share

I have a user whose workstation is in a domain
called "newnt". When they go thru network neighborhood,
browse the domain, and double click a particular server
(windows 2003) they get the message "Incorrect password or
unknown username". If they enter "newnt\JSmith" and their
domain password, they get signed in. But just "JSmith"
and password does not work. Why is it asking for the ID &
password, and why does it work with a domain name? The
server and the workstation are in the same domain.

Thanks