Stored username and password

I hope this is the right thread to post. If not please advice

Configuration Scenario (Vista Business version)
Under User Account / Manage User Password, I've assigned a *.domainname
so that when I map a network drive within the same domain, it will use the
stored username and password to access resource. This works in XP without
any issue.

Problem
When I then manually assign a map drive, the credential prompt for username
and password comes up. Why does this come up even though I have done (2) as
above. I want Vista to use the configuration I did above as in XP so any
resource requiring password will be obtained from there.

I can get round this by not doing the configuration above and go straight to
assigning the map network drive. Once the credential prompt comes up, I
enter the relevant details (which gets saved in the Stored username and
password), and I can see the resource. This would be a permanent setting
and Vista will remember the username and password next time I access the
same network drive. But am I missing some steps on Vista if I want to rely
on my configuration above? Nothing I did was different to XP setup.

Is there a fix for this?