rc.0 scope or other shutdown scripts in this distribution?

Hi,

This is for a little cluster computing project using tomsrtbt.  I'm trying
to get the rc.0 script to remove the machine ip address from a file that it
registers it's ip address with at startup on a cluster master node machine.
The scope is such 'halt' kills the mounted nfs share that I've been doing my
master-slave node communication over, before it runs the rc.0 script that I
have tried to run my commands through.  Is there another alternative to rc.0
or a hack that will make it execute another script before 'halt' kills the
nfs shares?

thanks,
Ian