dial up DNS

I have got a modem working on ttyS2 and have been able to connect to 
SBC-Yahoo thru the 'Debug' button in Dial-Up Configuration.  I can ping 
using a numeric address but cannot get dns service to work.  I have tried 
both selecting 'server provided DNS and putting in a known DNS server 
manually (though it is a different ISP's dns server - not SBC-Yahoo's - I 
don;'t know theirs and am afraid to ask).
Also and probably unrelated if I use RedHat's dialer from the Gnome menu it 
sits with a message 'waiting to connect' forever.  I left it for 20 min. to 
see if I could get some kind of failure message but none was ever 
presented.  Thanks for any help.  BB