How is 'pppd' launched while starting

[Guo Jiahua <gjhdgm@gmail.com>]

Hi, everyone,
I'm a user of DEBIAN 5.0. And I use adsl to connect to the Internet. I
think pppd is the key program to connect.
My ISP requires a MAC address which is different from my laptop.
So, I think, I must change the MAC address (by using command "ip link
set ethX address XX:XX:XX:XX:XX:XX") before pppd launched when starting
up
Thus, I wander how is pppd launched while linux starting, by a script in
'/etc/rc*.d/' or in other way.
Thank you very much.