Joining a Windows Xp pro to a Windows Server 2003 is quite as easy as one two three as long as you follow all the requierements of joining a workstation to a domain. But what if following all the instructions on how to join a Windows Xp wont let you see the "Welcome to the new Domain" info? Well here are the common reasons why you were unable to join your Windows XP to your Domain:

Primary DNS address is not configured correctly on Windows XP pro.

You can not join a workstation to the domain if the DNS configuration of your Windows XP does not point to your DNS server address. You will not be able to ping your Primary Domain Controller using its FQDN Fully Qualified Domain Name such as srv1.mysite.com (mysite.com will be the name of your domain) because no one will translate the ipaddress of you Server to your Server's hostname or FQDN.  So if you try to join your workstation to mysite.com domain you will receive an error.

If you misconfigured your DNS address . You can still join your Windows XP to your domain simply omit the .com extension on the name of your domain so if your domain name is mysite.com  just enter mysite in the domain text box but after joining it to your domain you will notice a slow network connection on your server.

Firewall is enabled on your  Windows Server 2003 Primary Domain Controller.

You have configured all necessary requirements done setting up and configuring a DNS server, assigned the IP address of the DNS server to your WIndows XP, enabled the NETBIOS over TCP/IP, you can now ping the server name or hostname as well as the FQDN of the Primary Domain Controller but you were still unable to join your workstation.

Furthermore, You checked the Event Viewer of your Server and found out that its 100 percent  healthy and no errors were reported. If you run into this situation check if Firewall was enabled on your server built in firewall or anti virus firewall because it is definitely the reason why you can not join your WIndows XP pro to your WIndows Server 2003 domain. Simply disable it and then after joining the workstations you enable it back.

DNS Server is not working properly

Check if your DNS server is working properly. Open the Event Viewer on your DNS server and see if there are errors in the DNS log entries look for critical errors. If critical errors were displayed then you have fo fix it first before you continue. You may uninstall DNS and reinstall DNS if need be.