Is the card "left over"? Then go ahead, you can only break something that isn't worth anything.
But... usually you can't flash 'em back. If something went wrong the card could be totally useless, and buying an original 7000 PCI Mac version can't cost too much now.
I've heard that this doesn't work on the PC cards, and the website seems to indicate that too. However, if you don't care about the card, and are willing to lose it I'd say go for it. But if you can't afford to lose the card don't try it. If you do flash it, and it works, let us know okay?