Hopefully the OP is still here and with us.
If so...
Ignore the modem driver - you do not need the thing
Focus on getting the NIC working correctly, then ignore Mandrake's (what I consider to be) shonky ADSL setup via MCC.
Instead, open a console and use
adsl-setup
as root
then to make it work
adsl-start
to stop (useful if not on a static IP and your connection seems to fail
adsl-stop
also of help if on a dynamic IP
route add default gw xxx.xxx.xxx.xxx
from running ifconfig and using the values for ppp0