start a process at boot up time

Hi,
I have a program that check the IP address and automatic update it to the DNS server. I would like to run this program when the computer bootup after pppd get a connection. How do I add it to the init file. Does any one have any information of how to do it.
I run a Linux Mandrake as a web server.
Thanks,

The scripts in /etc/ppp/ip-up can be modified to perform work after an ip address is acquired. From the pppd manpage:

/etc/ppp/ip-up

A program or script which is executed when the link is available for sending and receiving IP packets  (that  is, IPCP has come up).  

It is executed with the parameters

interface-name tty-device speed local-IP-address remote-IP-address ipparam