I have an idea, but it's a long shot...
there's a service in the UK where you dial a number on your mobile phone and place it next to a speaker playing a song you what info on. If the "thingy" at the other end of the phone recognises the music you get the information texted to you.
http://www.shazam.co.uk/music/portal/sp ... gging.html
So if you can get the song off the cassette and onto an mp3 I don't mind downloading and playing it to see what happens. You only get charged if the service recognies the music and even then it's only 50p so it's hardly gonna break the bank.