workgroup vs domain… ??

I have 10 pc workgroup including a win2k server. ” the server” is used as file server only.
I also have a Router/firewall with DHCP enabled to provide access to the internet for all PCs.
I want to promote my win2k machine to a Domain controller sothat users can login from any pc on the network and access their resources.
i’m not sure how to handle the DHCP server issue.can you please help??