Win 2003 Server (DNS) and Active Directory/User Account

I Installed Win2K3 and Contifure A/D and DNS for xxxxcorp.com.
I’ve Created user Profile in A/D. I have 3 Win XP Work Stations.
1. When I try to log on XP Client 1 for Authorise user it take very long time to log on some time (whole night).
2. On 2nd and 3rd XP Clien it dosen’t see the domain by (Domain server did not accept the request).
What am I missing? or How to configure the DNS correctly.
Any help or guidence…Appreciated.