Hi Mark,
We have a large number of VLANs here, so in order to get around creating several different OScustomization's I have a single OScustomization which uses DHCP. This allows the server to boot, apply the OScustomization (join the domain etc), then once this is complete the second part of the script changes the VLAN and sets a static IP address which networking configs (gateway) which are specific to the final VLAN.
Thanks,
Duncan.