Why cant i contact my domain controller

I have huge difficulty adding my pc to the domain. I have a windows xp service pack 2 (computer name is xpmachine) and want to add this to the domain in server 2003 ( domain name is contoso.com). I did add this computer in the contoso domain and have assigned IP address to my xp and aslo entered the DNS IP in the DNS server tab of the Advanced properties of my TCP/IP netwrok.
when i want to add the xp in the domain by going thourgh the Network ID of My Computer Name it gives me the error:

“A domain controller for the domain CONTOSO.COM could not be contacted.”