all you need to do is add the in the nameservers that you want to use
i.e
for me (i use telstra), i would do this
nameserver 61.9.240.13
nameserver 61.9.240.16
search wa.bigpond.net.au
then depnding of which version of e-smith you are using, you rebuild it using one of these commands
for e-smith 5.5 - /sbin/e-smith/signal-event console save
for e-smith 5.1.2 - /sbin/e-smith/signal-event console-save
that will rebuild all of the configuration files
there is a quicker way, like just to rebuild the resolv.conf, but im not sure how to do it

hope that helps