Are you using the built in PPPoE in OSX, or did you install their PPPoE software? You should use the native PPPoE OSX driver. If you are using built in PPPOE what are the PPPoE settings? It should have:

"Connect Automatically when starting TCP/IP applications" checked on.

"Send PPP Echo Packets" checked on.

"Disconnect when user logs out" should be checked on but is optional. Nothing else should be checked here unless you really really need it.

Under the TCP/IP Tab, what does it say? It should be configured "Using PPP" and not something else. It should show an IP address provided by the PPP server, and the domain name servers (optional, but if you are only able to ping IPs and not the domain names, you may have to fill this in from the ISP) also the search domain should be filled in to whatever the ISP assigned to you roadrunner.att.net or whatever. If you don't have a DNS server entered, put in 1.0.0.0 and 1.2.3.4 and OSX should automatically detect them and fill them in for you. If not, then your ISP isn't issuing DNS servers via DCHP to your box. Call tech support and get the IPs of the DNS servers to enter here.

It sounds like your DNS got fscked up somehow. What is it set to?

Anyway Inside the Apple menu choose System Preferences and then click on the Network Icon, and then click on the TCP/IP and PPPoE tabs and verify what settings they should have.

Good luck, I hope it works! Last Feb I did OSX support for SBC DSL at the Help Desk at the Big C company that they contracted it out to.