This card gave me fits with redhat 6.2. First off, it doesn't run in PnP mode, so I had to dig up a copy of the software, then a copy of DOS to run it. I used FreeDOS (I have only NT lying around).
To add to the fun, the FreeDOS distribution doesn't currently work if you don't have a writeable C: drive. You get an error about not being able to open c:\Freecom.log. The FreeDOS website mentions this many times, including a note about the maintainer being annoyed at getting asked the question so much. Perhaps he wouldn't get so many questions if he's actually just put what to do in the FAQ or something...anyway, the answer is that it's a bug in "FreeCOM", the command.com replacement, and to fix it, you must get a newer version. The site doesn't tell you where to get it, but a quick Google search turned up sourceforge as the repository for new versions. This is probably fixed by now.
For some reason, RedHat didn't install the network card correctly, so eth0 failed to initalize. An "alias eth0 3c509b" in /etc/conf.modules loaded up the driver as a kernel module. The driver still failed, because it appears that for some reason (determining this by running insmod on the command line with the module) despite what the docs seem to imply, that driver would not accept io= as a parameter. Perhaps I had the syntax messed up, but removing the options in conf.modules for the io port and irq cause the driver to find eth0 and be happy. Kind of strange. You may have to put the card at the default ISA settings in order to make it work without configuration parameters.