ok, I tried everything and it won't work as I want it:
- the realtek drivers crash after a several time under the newest OS X.
- the macsense driver allowed me only 10 Mbit speed with a 100 mbit card!
So I'm again at the beginning: are there any working drivers for realtek 8139 100 mbit ethernet cards?
Under MacOS X 10.4 (in the good old times *g*) the drivers worked very well, but now...