Someone recently posted a similar message on a different message board. They recommended entering all TCP/IP settings from scratch instead of copying the settings file over from another System folder. You're on DSL; have you ever used IPNetRouter? It patches the TCP/IP configuration with a reference to an IPNR System folder file. If that file is removed (like if you did a clean OS install) then your IP won't work. To fix this, create a new TCP/IP configuration and re-enter all config info from scratch.
Or have you done this already?