I have reference sources listing "Ximena" either as being a Spanish feminine version of "Simon", or being Greek and meaning "heroine". Like Pavlos, I can't fathom the Greek connection either. Other reference sources simply come right out and say that the origin and meaning of the name are "unknown".
The historical Ximena was the lover and then wife of El Cid, and her name also appears sometimes in the Basque form of "Chimene".
Mike, I love your new FAQ. This, though, cracked me up: "RTFM stands for Read The First Message (though it stands for other things elsewhere)..." :)