With all due respect, the attribution of any of those swords to King David (i.e 7th-8th century BCE!) is the most ridiculous of all. I would challenge anyone to produce another iron implement from that era that managed to be preserved in such an intact shape and to be executed in a style of 10th-13th century CE!
I have deep respect for people's religious beliefs, but the tendency to bolster their claims for authenticity by producing clear fakes has nothing to do with ethics, philosophy and law(that in fact comprise the definition of religion). This is pure snake oil and brings only dishonor and ridicule.
As a matter of fact, we already had this discussion and Yannis brought a beautiful link to the pictures of the Swords of the Profet.
See for yourself.
http://www.vikingsword.com/ubb/Forum1/HTML/001968.html
I fully appreciate the danger of converting this debate into something very ugly. I trust that all of us (I can vouch for myself) are motivated by purely academic and factual motives. Anybody's religious beliefs are his/her (you see, I am politically correct) private business and should be fully respected; validity of historical and material artefacts is a part of public domain and can be vigorously discussed.