Enable Network sharing w/o bootpd becoming active

Hi All,

How do I get Leopard (10.5.8) to do IP forwarding and NAT, but NOT serve dhcp address ?

This did not seem to be a big deal to me until I was not able to make any persistent edits to the plist files that control the bootpd server.

The setup:
Two preexisting networks one on a reserve block, one routable, both fully functional with the normal complement of dhcp/bootp, time, nfs, afs netbios etc services running on them.

One MacPro is dual homed and sits on both nets.
I want to use the macpro as a simple NAT gateway to allow the reserve block ( internal) net to reach the rest of the world.

Simple you say, just click on the Internet sharing to turn it on, and your done… and your right….
Except that as part of turning on the sharing OSX also turns on a dhcp/bootp server, which now tries to answer requests from the internal net causing great confusion and breaking things .

Again easy fix, just tell the bootpd server to not assign addresses…
Except that the bootpd.plist file is dynamically generated and will not allow the change.

The *NIX admin in me keeps saying that there must be a shut-up-and-do-what-I-tell you button, tha will let me turn off the bootpd service with out messing up the rest of the setup. But I’ll be damed if I can find it.
Or possibly I have to use some other function, or not use the GUI to control this… either way I’m lost.

Thanks for any help.
–Bill