Modem Connexion With Inmarsat M4


I have a powerbook with mac osx 10.4.2 and a usb isdn webshuttle II modem from Hermstedt. I would like to use it to connect the mac to internet via an inmarsat M4 station.
I have the latest driver from hermstedt (mentioned to be compatible with 10.4) and the webshuttle is recognized by the Mac. But none of the modem scripts (even the inmarsat script) function with the modem. The mac froze when i attempt to connect to internet. No kernel panic, but impossible to do anything, just reboot.
I send a mail two weeks ago to Hermstedt, but i have not received any answer yet.
My inmarsat M4 works well with a com1 isdn usb modem (no driver for the mac) and a PC under windows 2000 or XP home SP2.
Any idea.