Double check you DNS servers. Is the address resolving correctly? If you're behind a firewall, you could be resolving to any number of IPs assigned to a particular domain.

If this is on an XP machine, I've had problems in the past with weird issues regarding DNS when an IP is obtained via DHCP. Static assignment fixes it, but I've never figured out the root cause.

On a side note, what are you trying to accomplish integrating AD with DNS? Is it some sort of corportate resolution method for LDAP?