justyn-

If the subnet mask you typed in your original post is in fact configured on your network as 255.255.0.0 (not 255.255.255.0), then in effect you have created one large LAN of 65535 addresses (a supernet, as opposed to a subnet). Essentially all address in the range of 192.168.0.1 – 192.168.255.254 are valid on each of your ‘subnets’. When you connect the two subnets together with a hub, you are creating one giant broadcast domain that overlaps which can lead to all kinds of odd problems and performance issues.

Not knowing how your network is designed, I can only offer a few ideas based on the info you’ve given thus far. Please take these options with a grain of salt as I might be barking up the wrong tree based on some assumptions I’m making…

Suggestions:
A — Fix the ‘supernet’ issue
– remove the hub
– give each subnet a mask of 255.255.255.0 thus cutting your LANs down to a more reasonable 254 usable addresses, i.e. 192.168.167.1 – 254 & 192.168.168.1 – 254
– now you’ve truly created two subnets…the problem is now you’ll need to route between the subnets for any communication to take place

B — Fix the routing issue
Options:
a) buy a cheap router (a multiport dsl/cable router would work) and configure it to pass traffic between subnets, then plug the two subnets in and try pinging to verify…you might be able to use your Airport Extreme for this by fixing the IP of the ethernet interface to one subnet while providing wireless connectivity to the other subnet…not sure though as I’ve never used an Airport station. The router will isolate DHCP requests to the subnet the requesting machine is physically/wirelessly connected to, so it should allow you to run a DHCP server per subnet as you currently do. Printing to the next subnet should be simple if the router IP for the respective subnet is used as the default gateway…if you already have a different default gateway, then you may need to fiddle with adding static routes. IIRC the Airport Extreme can provide DHCP services, so you might be able to offload this from the XServe if you so choose.

b) pick one of the XServes and dual-home the network connections, i.e. connect one ethernet port to each subnet and IP the interfaces accordingly. Enable DHCP on this server and create two scopes, one for each subnet. Disable DHCP on the other server. This should provide for DHCP addresses to be served on the respective subnets. Configure print queues on the dual-homed XServe to be used as a print server for the common printers.

C — Ignore everything I’ve written and leave your network alone. Go to each DHCP server and create address ‘reservations’ for every device that will pull a dhcp address. In essence you will be tying an IP address to the MAC address (hardware address) of the network port on each client. This way your client systems will always pull the same IP from DHCP. You just have to remember to do this every time a new computer gets added to the network.

Hopefully that’s somewhat coherent…it’s a tad late as I’m writing this up!