I think when you install realplayer, you let it associate all your media files with it. But for the .avi files which is the most popular file type the dvd you rip to, you should really just use windows media player to play it. Don't know how Kingsoft's media player works, So here is the conclusion,
( 1) If you use Windows NT 4.0, you probably can't play it. Because windows NT 4.0 doesn't support div4. Otherwise, find div4 codec and install it.
(2) play the file with WIndows Media Player
More questions, let me know