Assumptions: RedHat Linux; Roaring Penguin PPPoE

Roaring Penguin sets up files

/etc/init.d/adsl
/usr/sbin/adsl-start
/usr/sbin/adsl-stop

You need to do

cd /etc/rc3.d
ln -s ../init.d/adsl S70adsl
cd /etc/rc5.d
ln -s ../init.d/adsl S70adsl
# This makes the automated startup config match the GUI config
cp /etc/ppp/rp-pppoe-gui/Home.conf /etc/ppp/pppoe.conf

Check to make sure that networking comes up automatically upon boot.

Get a hostname from dyndns.org.

Get ddclient: http://burry.ca:4141/ddclient/ddclient-3.5.4-1.noarch.rpm

Make sure that ddclient exists in /etc/init.d.
cd /etc/rc3.d
ln -s ../init.d/ddclient S71ddclient
cd /etc/rc5.d
ln -s ../init.d/ddclient S71ddclient

- Edit /etc/ddclient.conf
- Uncomment "use=if,if=eth0" line and change it to read "use=if,if=ppp0"
- Set login, password to dyndns.org login, password.
- Uncomment server line for dynamic addresses, replace
  your-static-host.dyndns.org with your DNS name.