QuickTime asking to reinstall additional software

Please help me solve my problem while trying to play a downloaded movie. By the way, I am using Windows 7 Professional. I receive this particular warning message saying that the document could not be opened. Further, it says that the movie I am trying to play is not in a format that QuickTime Player understands. It also says that there is the need to install additional software to open the file.
I know that there could be lacking application in my system, but I do not know what it is and how am I going to have it. When I click on TELL ME MORE in the warning message, I only get information that does not come to my understanding.
The document “M2U00001.MPG” could not
be opened. The movie is not in a format
that QuickTime Player understands.
You may need to install additional software to open this type of file.
Tell ME More OK
