Can work with the free, legal and cracked version of NT7 !!!
Menu of NinjaTrader : File -> Utilites -> Import NinjaScript...
you may use another way for import addons:
For it simple extract files with extension .zip and copy/replace all
extracted files into folder "C:\Users\xxxxxxx\Documents\NinjaTrader 7\bin\Custom\"
For extract ZIP archive you can use WinZIP or WinRAR software or any other program which works with archivies.