What is twixtor exactly? If I download it will it harm my computer?
Twixtor is a plugin for a lot of different NLEs.
From the web site:
Twixtor intelligently slows down, speeds up or changes the frame rate of your image sequences.
It's very good at what it does and consequently is not cheap.
http://www.revisionfx.com/products/twixtor/ for more info.