If I launch ethereal from KDE under a normal user logon, I get no interefaces to choose from. If I SU to root and type ethereal from CMD, ethereal gui comes up and I get all the interfaces. What do I need to give my user permissions to?

Hi

Only root can put the interface in PROMISC mode , so that your ethcard will pass the packet to the kernel even if the destination hardware is not yours.

So be sure to untick the "Capture packets in promiscuous mode". I think its not your problem.

What happens with this? (assuming you want to listen to packets which are aimed at eth0):
tcpdump -p -i eth0

If I SU to root, and issue that command I see all kind of packets. I uncheck "Use Promescuous Mode" and I still have the problem. I have no interfaces listed. The interfaces are listed if I lauch the program from root, however.

Strange..
Maybe you are using an old libpcap? ldd `which ethereal` | grep pcap

Is the user able to use the network, like browsing,... ?

matt@monet:~$ ldd 'ethereal-0.10.12' | grep pcap
ldd: ./ethereal-0.10.12: No such file or directory

Thats what I get...

I am able to use the net and use SAMBA, etc.

You have to type exactly this:
ldd `which ethereal` | grep pcap

Maybe it will be easier to post to ethereal forums or to pcap forum.

Or (what I would do) you take the version of pcap you are using, you get the source and you try to see what happens in the function pcap_list_interfaces or something like this.
In general, for getting list of interface or hw adress, you open a socket (thats why I asked you if the user had network access) and then look which interface is used... and so on.

Last idea, more quicker , you can try
$strace -o /tmp/ethereal.strace ethereal

and then look in ethereal.strace to see why/which system call fails.

you may have to get strace from somewhere, it is a very helpful tool for tracking problems.

Bye