DNS and DHCP

I have a flat vlan network with all NT servers. I have setup a WIN2K server with AD/DNS in it’s own domain planning implementation of exchange 2000 on that server. DHCP/WINS resides on an NT server. All subnets are accessible anywhere on the network. If I use static entries on my WIN98 clients I can ping the alias of my win2k server. If I let the client get IP via DHCP, I can’t ping the alias name, only the IP. I use an external DNS and want to put this server on for local DNS. I have entered DNS on all subnets in my DHCP GLobal options. Why can’t I ping the alias of my win2k server when I use DHCP for IP?