Can’t add XPs to new w2k03 Domain

Greetings,

Configured a new test Domain server. DNS installed and nslookup is fine. None of the Workgroup XPs can join the domain:

A domain controller for the domain xyz.com could not be contacted…

1-All settings for preferred dns point to this server.
2-nslookup on xp fails for domain box lookup.
3-dns records on DC correct.
4-dynamic lookup: nonsecure and secure
5-/flushdns and /registerdns on DC and xp
6-using dsl router BUT tried adding using switch only
7-have sp2 for w2k03 server installed
8-ran dnsdiag on server: all pass
9-ran dcdiag on server: all pass except DHCP but static IP on all boxes

Please HELP!