RHN Update

[Brad Carpenter]

OK, basic question here, we are running RHEL3 AS using it for ISP functions,
last time I connected to RHN it wanted to download a caching-nameserver,
which I did, which took over and made our secondary DNS server "fall off the
map". 

We recovered fairly easily, albeit very nervously, and wish NOT to run into
such problem again.  

Question is "Are there updates that we should ignore on a system like this?"
And if so, how does one go about picking and choosing what to skip and what
to keep?

I see posts that say "update everything" all the time, is this the way it is
expected to work?

Brad