Hot to run a script upon connecting to the net

[Federico Tello Gentile]

Hi everybody.
A quick look at the archives did not answer my question.
How can I run a script (with root permission) when I set up ppp0 with my 
dial up account?
I use the system-control-network tool to dial up. I see there is a up-ip 
script in /etc/ppp/ but it is not being called.
Any simple way to start the firewall (i.e. run "firestarter start" as 
root) when the connection is up?

I run FC 2 and I have an internal isa (8 bit, pnp) modem that Fedora 
sees as a regular serial port. It does not detect it as a modem (but it 
is not needed).

Thanks.