Further to above: the following should fix the nic_config_tivo problem for modem setup (note, Warren may make an update available for
'update_oztivo -y' download):

Edit /sbin/nic_config_tivo and replace line 269:
[i.e.
cat $pppops | sed "s/^user.*/user $username/" > $pppops || \
fatal "Cannot update $pppops"
]

with:
cat $pppops | sed "s/^user.*/user $username/" > $pppops.tmp || \
fatal "Cannot update $pppops"
mv -f $pppops.tmp $pppops


To edit above file you'll need to make the filesystem read-write using:

cd /sbin
rw

...then edit and save /sbin/nic_config_tivo as above. Make sure nic_config_tivo is executable using:

chmod 775 /sbin/nic_config_tivo

then set filesystem back to read-only using:
ro

Then nic_config_tivo should correctly create/update the following 3 files for the modem option:
/etc/tclient.conf
/etc/ppp-options
/etc/pap-secrets


Cheers,
Martyn.