use File::Basename;

 foreach (<DATA>) {
          chomp $_;
          ($file,$base,$ext)=fileparse($_,qr/.[^.]*/);
          $file =~ tr/\./\_/;
          print "Change: $_ to ${file}${ext}\n";
 }

__DATA__
test0.file0.new_20060411.zip
test1.file1.new_20060411.zip
test2.file2.new_20060411.zip
test3.file3.new_20060411.zip