Networking between WIndows Vista and Windows XP

Hello everybody.
I have two computers: HOME(with windows vista) and OFFICE(with windows xp),
in HOME i can see all the pcs, i mean i can see OFFICE pc and its sharing
documents including the printer (it's local installed in OFFICE); but when i
try to see HOME from OFFICE only i can see the pc but when i try to enter to
HOME from OFFICE it ask for a user and a password; when i installed Windows
VIsta i didn't configure any user only Administrator(Carmen) without a
password.
I don't understand why is happening it.
Thanks