Ok, thanks a lot for the kudzu trick !
For info, i've been trying for a few minutes now a Xircom Realport Cardus RBEM56G-100BTX on my compaq 1598DT Armada with a stock Mandrake 7.02 (air), with default pcmcia package 3.1.9 and both function of the card seems to be working ok !
Writing this message on the net by modem while copying some stuff on the LAN :-))
Anyway, at the beginning, the ethernet part seemed OK, but the modem didn't ! I then remembered the kudzu trick which solved the problem and now everything works together.
Well, i will go through a bit more testing but up to now, i am happy. I don't know much by now about how the RBEM56-100 will act with suspend etc...
Thanks to everyone on this forum and specially to David for his fantastic work !