it all depends
What you need is a little more information for us to feed on, il try to tell you where to start
but there are many more qualified people here that can help.
does your isp use DHCP to assign client ips? or do they tell you what your computers address should be? Howabout name servers? do they have one or do they refer you to someone elses. Fire up redhat-config-network/neat: this is where you put stuff into the blanks, theres a button for DHCP and one for Server assigned nameservers, or there are blanks to fill out, apparantly you already know that, but gee i sure do love to type.