trying to connect a third computer

I have Qwest DSL and an ethernet with two ethernet connections......they work
great but now I have a third computer next to one of my connections. Talked
to CompUSA and they told me to get a router to plug in the one connection to
make it into two. I have done that but it will not connect either computer.
I have restarted the D-Link in several different orders and followed the
instructions on the Quick Start. My biggest problem is that I am unsure if
my DSL needs to be a dynamic address and what information I need to put in or
if it is PPoPe or static address. I have tried all of them but now am
worried that I have given it too many commands. Can anyone help me.
Thanks, Rianna