About DHCP Sever in Windows 2000

Hi,
I have a question on DHCP.I have windows 2000 advanced server with active directory installed.
In my institute I have three different section.One is HR,second one is Front Office and third one is accounts.And all the computers are configured on DHCP they are getting IP from DHCP server.I have created three scopes for all the three accounts.
Scopes are:
Scope Name : HR
IP : 192.168.100.2 to 192.168.100.26

Scope Name : Frontoffice
IP : 10.0.0.2 to 10.0.0.35

Scope Name : Accounts
IP : 90.0.0.3 to 90.0.0.20

Now I want following department will get ip from their scope.But they are not getting it.

How do I configure my DHCP server and DHCP clients so that they will IP address from their scope.

I would appreciate if someone provides me assistance on it.

Regards.

Anurag.