I had the exact problem and not sure exactly how I fixed it. fist if your modem was ttyS4, use ./MAKEDEV ttyS4 to make it, then ln -s ttyS4 modem so kppp can see it. Try chmod 777 to both ttyS4 and modem. try route -n, while your are online you should get 2 lines and they both should end in ppp. try ifconfig eth0 down. try netcardconfig too. If you find out what did it post back. check /etc/resolv.conf to see numbers are good also resolv.conf in /etc/ppp. read man resolv.conf. Try to access google without name 216.239.37.101

Somewhere in there is solution. Don't give up.