Re: Win2k ad and Win2k3 ad co exit in same network?
What forest functional level is the Win2k3 AD running in? You may not install Win2k AD servers in a 2003 native or 2003 interim forest functional level forest. Your forest functional level for the 2k3 forest would need to be running in Windows 2000 mixed mode.
See http://technet2.microsoft.com/WindowsServer/en/Library/b3674c9b-fab9-4c1e-a8f6-7871264712711033.mspx?mfr=true for further clarification.