Realplayer and Apple’s Quicktime both take over your computer and eventually you come across a site that makes you want to install them…
There are free alternatives:
http://www.free-codecs.com/download/Real_Alternative.htm
http://www.free-codecs.com/download/QuickTime_Alternative.htm
They both come with a program called “Media Player Classic” which I use as a replacement to Windows Media Player. You can download the Lite versions which don’t come with this, but I think it’s a great little video player which is much more stable and speedy.