QuickTime X is the default QuickTime player installed with OS X Lion (10.7) and later.
You will need to install QuickTime 7 to play the subtitled movie*. You can also use QuickTime 7 to "burn" the subtitles into the movie so that it can be played with any player.
You can find more details here: http://support.inqscribe.com/knowledgebase/articles/37648
*NOTE: Due to security risks, we do not recommend QuickTime for Windows users (more on this subject here).