I forget the steps i took (mandrake was installed for only 2 days untill i gave up on it as an OS) to disable ipv6, tho in theory 10.1 should have fixed this so i cant confirm if ipv6 is at fault - worth a shot though.
You've probably already checked this but what about the connection speed in the kppp settings.

maybe try www.linuxquestions.org, its a good site for those sorts of things