Have you tried re-installing all the network stuff again? I had a
similar problem with Insight, and this fixed it. Dunno why.
I had another similar problem - when I set the host resolution order
to DNS, Files, None, and rebooted, it would always revert to something
else (can't remember what, probably NIS, DNS, Files) so that it didn't
work. Dunno what I did to fix that - just one day it started working
so I left it!