According to one of the comments at newegg, it won't.
Only works with ATI video cards. The sales language is not strong enough, saying that it works with ATI cards. But you MUST have an ATI for this to work. Definitely does not work with GeForce card in MacPro.
Of course we can't trust such comments, but I do remember reading somewhere that these adapters actually do convert the signal or transcode it or something. I honestly don't remember what it was saying, but I do remember reading an explanation as to why this adapter wouldn't work with anything but an ATI card.
The first few posts in this thread indicate the aforementioned claim on adapters.
The link above doesn't seem to work right in the forum. When you click it, remove the "[url]" that comes before www.avsforum.com/
in the url.