Go to http://www.playlist.com/?home=a&redirect=true
Make an account, and find your song there, if it is a common enough song, you'll probably find it. Follow the instructions on how to make the playlist and post it. Make sure to check the a off, coz some guys here don't like that (as we've learned in half a dozen threads... LOL). NOTE: The embed format for MySpace works for RJ.
Just edit your profile and add the embed code into the About Me or Who I'm Looking For section in your profile. Save it and test to see if it works.
If the song you want can't be found. Upload it to to here: http://www.upload-mp3.com/
and then copy the direct file link it will then provide. And click on the Add Song by URL button in Playlist.com and use it there.
This is an example of a playlist made from both those sites: