DSL modem disappears after sp1 install

I have downloaded XP sp1 but after it reboots to finalise the installation it
shows no modem and the drivers will not reinstall because it doesn't see a
modem connected to the system. The sp1 itself shows no problems and installs
fine and when I uninstall sp1 my modem "like magic" is back and working fine,
I've tried the AOL helpline and they said they haven't a clue what it can be
and advised me to just do without the sp1 update(great eh!). The connection
is PPPoE, I have reinstalled the AOL software, the modem software (which is
all on the AOL CD), I have updated the modem software, I have tried sp1 and
sp1a all with the same results. HHHHEEEELLLPPPPP please!