You can apply Group Policy settings to XP machines, the process is a bit convluted however.

You will need to obtain poledit.exe from an windows 2000 or above server disk. This utility will allow you to use group policy templates to set options. Run poledit.exe on an XP machine logged in with a local account to a network account. Save the poledit.exe file as NTCONFIG.POL and place it in the /private/ect/netlogon directory of your OSX server. XP (NT & 2000 as well) automatically check the netlogon folder of their domain controller and look for a NTCONFIG.POL for a group policy setting. You are able to apply group policy’s by Machine, User Group, & User. I have been running this without incident for almost 2 years and it works great once you get it going.

You may need to edit the group policy templates a bit so POLEDIT.EXE will run them but some googling should yeild some guidance. You will also need to make sure that everyone has read access to the netlogon directory.

Good Luck