win 2k DNS dynamic update problem

please help. My network includes DHCP,DNS and DOMAIN CONTROLLER.DNS DOES NOT DYNAMICALLY UPDATES THE THE A RECORD BUT THE REVERSE LOOKUP ONLY.I checked the options in DNS AND DHCP TO MAKE SURE THE A RECORDS ARE AUTOMATICLLY UPDATED BUT STILL NOT WORKING.I ALSO CHECKED THE TCP/IP CONFIGURATION ON THE WORKSTATION PROFESSIONAL.WHEN INSTALLED THE DNS I CHOSE PRIMARY .I EVEN USE THE COMMAND IPCONFIG/REGISTERDNS, STILL NOT WORKING.WHAT IS THE PROBLEM? PLEASE HELP