Rosy,
We cannot call you from this forum. If you truly need a call, you can open a TAC case. The info I can tell you is that you need to fix this in your dns. A simple google search of "no SRV record Windows 2000 server" comes up with numerous resources that can help you fix this. Here is just one example.
http://support.microsoft.com/kb/241505
and
http://www.petri.co.il/active_directory_srv_records.htm
I would also advise you, if you are doing a new install with Unity 7 and that version of Exchange, that you use Windows 2003 as the OS. Even MS doesn't support Windows 2000 Server any more so if you end up having an OS issue on your Unity server, we will not be able to get MS to help you. From a support perspective, I would advise you to use Windows 2003 Server in this implimentation.
Thanks!
Tray