Problems relating with server connectivity.

I am having lots of trouble with my server. One problem is the connectivity problem between my DNS and SL.
I cannot play my Snow Leopard unless I use DC as the only DNS server. Another problem is that my SSO cannot function properly after trying every troubleshooting. It regularly asks for authentication before I could log in.
Given that the configuration of my network of Mac is connected to older Windows 2000 Server AD environment.
Why is it that I encounter such problems?
