converting quicktime videos to windows media player

You send the file, not the video player. Also, nothing stopping you from installing and using QuckTime on Windows.

You neglect to mention what file type you want to convert from and to. Probably .mov for QuickTime? There are others. For WMP, also a slew of file types available. mpeg? wmv? Regardless, there are tons of converters (and media players with converters built in) freely available. http://www.google.com/search?q=convert+mov+to+wmv for example.
Don't install anything from un-reputable sites, and you shouldn't need to buy anything (unless you want a well-known video editing suite).

http://www.ehow.com/how_6358485_convert-mov-wmv-vlc.html