To force the client machine to get the recent group policy from the server use the below options,
For 2000 Clients :
* SECEDIT /REFRESHPOLICY MACHINE_POLICY /ENFORCE:
Immediately imposes group policy object settings located within the "machine" node of relevant group policy objects.
* SECEDIT /REFRESHPOLICY USER_POLICY /ENFORCE:
Immediate imposes group policy object settings located within the "User" node of the relevant group policy objects
For XP Clients:
gpupdate - To update the group policy in the client machine.
gpresult - To view the resultant set of applied policy to the client machine from the server.