That was unbelievably simple, to change the server. Just went to server manager in the admin tools and made the server primary, waited a couple of mins while it did it's stuff, rebooted and everythings happy.
I spoke too soon. The macs running OS Tiger cannot find the proxy server, DHCP server, the NAS or basically anything on the network. The mac running OS Leopard can. This is quite irritating to say the least. It just looks like I am going to have to upgrade them all to leopard. I have been through the network settings and nothing appears to work. Macs just confuse me at times.