DM111PSPv1 – ADSL2+ Ethernet Modem Set up

I'm trying to set up an older DSL modem.  We don't have cable internet yet but it's supposed to be coming through in the next year so I didn't want to spend the money on a modem I wasn't going to need.  I'm having a little trouble setting it up.  My first question is the DSL username and password, is this the same as the PPP username and password.  This is all that Centurylink would give me.  The other is the IP address.  should this be the private or public?

Thanks