To play a song in slow motion or slower than the original speed of the song, you will need to download software's from the internet which can help you to do this. There are many software's available on the internet the most famous being 'Winamp Pacemaker' these software's allow you to tweak the playing abilities of a certain song. You can control the tempo of the song as well as the pitch and key. There is also a tab to control the speed of the song. By adjusting this tab you can manage the speed of the song and adjust it to your desired speed. However keep in mind that by adjusting the speed and playing the song in slow motion you will loose out on the vocal and musical quality of that particular song.