DHCP Clients/server and Debians IPMasq package

[Simon Higgs <please.use@reply.to>]

[Also posted to linux.debian.user]

I have an old 486 which i'm using as a 'broadband router' for my cable
service. It has3 nic's. One connects to the cable modem, and obtains 
it's IP via DHCP. The box also runs a DHCP server, which allocates
IP's to the other two nic's.(192.168.1.0/24 and 192.168.2.0/24)
Finally I have the IPMasq package which I am using as a start point
for the firewall.
Although my (isp) allocated IP has only changed during re boots of the
router, it is a dynamic service.
This surely will break the ipchains ruleset produced by IPMasq?
How would I ensure '/etc/init.d/ipmasq restart' is run if my IP
changes?

TIA, Simon.