Accessing other domain computers from Vista

I've run into a situation of late (not really a problem) regarding accessing
domain computers from a Vista workstation.

Our LAN consists of about 25 computers running Windows 2K or XP with one
exception. My workstation runs Windows Vista.

My login has domain administrator authority. All computers within the LAN
have one or more folders set as shared to the domain administrator as well
as my login so I can access these files from my desk.

If I login to any Win2K or XP machine using my login, I can see and access
any computer in the LAN by merely clicking on the name and going straight to
the folder.
At one time, I could do the same from my Vista machine, but as of late, I
get a popup asking for me to login to each machine with a valid login name
and password. The only login it wall accept is the specific administrator
account for the machine in question.

My questions:
1. Why has Vista all of a sudden required me to use logins to access the
other network machines and how can I change it?
2. Why will the other machines not accept either domain admin logins or the
machine's primary user login when I access them from the Vista machine?


Thanks in advance,

Ron