I'm running BeOS Personal R5.03, and it's
working great, except for some known issues
with my onboard sound (AC97, I'm aware of
the problems with it), and networking is
not working properly. I have a linksys
LNE100TX version 4.1 PCI ethernet card.
Under the Devices settings, it appears that
the card is being properly detected, but
under the Network settings there are no
interfaces listed, and even after manually
entering all the necessary IP's, I am
unable to connect to the internet. I think
BeOS only officially supports the LNE100TX
up to version 3, is anyone aware of drivers
for version 4.1?

I've posted a screenshot of my settings at
http://www.appstate.edu/~ec50246/beosscreen.png.

Ive seen many people who have trouble with their linksys cards. And rev 4 is not supposed to work at all under BeOS.
You might be bettre off with another card.
A cheap solution is a card based on the realtek 8139 chip, comes around 10$ in the cheapest versions and works flawlessly under BeOS. Other cards I've used with success under BeOS is Netgear FA310TX and Davicom based cards. In the more expensive field 3com is the winner.