What song? That link just took me to a forum.
To turn a song into a ringtone;
1) Open iTunes and go to Preferences
2) Go to Import Settings. Where it says 'Import Using' make sure AAC Encoder is selected and then click OK.
3) Add the song you wish to use as your ringtone to iTunes
4) Right click the song and select create AAC version
5) Drag AAC version of the song you just created to the desktop.
6) Select the song and change the file extension from m4a to m4r.
7) Drag the song back to iTunes and it should now appear under ringtones.
8) Sync your iPhone with iTunes and remember to select Sync all ringtones.