can't resolv host name with firefox

[Antonello PAPA <anto.papa@xxxxxxxxx>]

I'm using FC4, I can ping an IP number but if i use firefox  i get the 
errore can't resolv host name.
Could you tell me what is wrong?
In another istallation of FC4 every thing went ok but in this one I can't 
get the web.
Could yuo tell me whict log file check?
tanks, Antonello.