I found this:
1. Open DHCP Manager on your Win2k3 server.
2. Right-click the DHCP server and select pre-defined options.
3. Click Add.
4. Set Name to IP Phone Boot Server.
5. Set Data Type to String.
6. Set Code to 156 and add a description, if desired.
7. Navigate to the scope options and add option 156.
8. Each option is entered witha comma as the seperator.
The following example would setup your scope with a management server at 10.0.0.1, with country as USA, language as English, VLAN tagging turned off & VLAN ID set to 200
ftpserver=10.0.0.1,country=1,language=1,layer2tagging=n,vlanid=200