Hello Terry Jones. If you enter Guantanamera in the DT and Forum search box and hit GO you will find out lots of information about this song. I can't recall for sure who had the hit with it, but it wasn't Pete Seeger, although as Little Hawk says he'd been singing it for years. Could it have been the Seekers?
There's a brilliant rendition of it on the double CD Estrellas de Areito;Los Heroes.
Try these links: Guantanamera
Thread discussion of lyrics
History of Guantanamera