I can't play any movies from sites like Rapidshare and others. And it says it's missing a plugin for Quicktime to play this movie, what plugin specifically.
Those sites may use some form of a Windows Media plug-in, which isn't natively supported by Apple, and Microsoft's old Windows Media Player for Mac isn't good anymore.
Try using these Windows Media Video components for Quicktime. This free program should help play most media out there.