Hi Samad,
Which version of Windows 2000 do you use? Have you installed Windows 2000 SP4? If no, I suggest that you upgrade your server to Windows 2000 SP4. A known issue with DHCP reservation display was resolved in Windows 2000 SP4. For more information, please refer to the following Microsoft Knowledge Base article:
328636 The Windows 2000 SP3 DHCP Tool May Show an Empty Reservations List
http://support.microsoft.com/default.aspx?scid=kb;EN-US;328636
Laura Zhang - MSFT