|Unless I'm misinterpreting what you need, which is to extract only the 4th line in the file, the perl command that ghostdog gave will do what you want. Did you try it?|
One change I'd make to it would be to add 'last' to it so that it doesn't run through the entire source file.
C:\>perl -ne "print and last if $. == 4" file > newfile.txt