In Vista (client machine), uncheck the IPv6 box in LAN Status box and set WINS to Enable Netbios over TCP/IP. Try to connect to domain again.
Another thing to try::
Go to the properties of network adapter
on client, choose ipv4 properties, add the internal addie of the DC t
the DNS and WINS server fields, located in advanced properties.
run "nslookup domainname" from client to be sure it resolves.