can't connect to Internet - DNS?

[rikona]

One of my 10.04 boxes can no longer see the Internet. Just happened -
has been working fine for quite a while. Nothing has been changed or
updated on that box, or the local net, or any other box. It can see
the other boxes on the local net, but not outside. Seems to be a DNS
problem. For some reason resolv.conf [on that box ] no longer has the
'nameserver' line. If I put the correct line there, save, check it to
make sure it is changed, and reboot, it is again gone. How can I get
it to stay, and/or fix this in perhaps another way? And, why did it
'just happen'?

In checking the net it is suggested to use network manager. I don't
seem to have network manager installed, even though Synaptic seems to
think it is. Do I need that tool to set this correctly?

Thanks,

 rikona