Cisco VPN Client keeps us out of new Xserve

We just got a new Xserve and it is set pretty much to the defaults. We have a client that we have to connect to via a Cisco VPN client on an OS X machine. When we are logged in to the VPN we cannot login to the Xserve. Our old NT machines are no problem. Is it something to do with DHCP? Something completely different? Any ideas?