Xvid is a very good avi codec and yes, it is perfectly safe. If you are interested in watching and making videos of your own, I suggest installing a free program called Format Factory. It installs almost every codec you would ever need and nearly all of your files will then play in the regular Windows media player. If you get Format Factory, you don't need to install Xvid since it's included along with Divx, H264, MP4, Matrosky, and a slew of other codecs.