How to manage Server NT,Win2K,2003

I just need opinion about my office scenario.
May be somebody can help me. I have 5 server in office ,currently use different OS but still windows. First one use Windows NT(PDC) others 2 use Win2000(BDC) and 2 other server use Win2003(BDC).Is’t correct we use this way or u all have suggestion.Co’z I’m worried about connection and network area. ok please…!