IDE won't open the .cpp file.
NewSoftSerial is listed on the libraries but not as a replacement, just an improvement.How are folks supposed to figure this out?
The prefix 'new' should provide a clue.
I don't see why the SoftwareSerial library example referenced on that library page is not included in the Arduino IDE download, on the Examples menu. It looks like an error to miss it.
The library IS included in the Arduino 0022 download for windows.
The fact that examples are not should be a clue for you to stop using it.