Personally, I've never heard of Ura Zelda until reading this thread. But I do remember looking through very early screenshots of OoT (much like that TV commerical a while back on this thread) that had the Medallions as equiptable items. I believe the one in the screen shot was the forest medallion, but that's not really important.
The caption that accompanied that shot said something along the lines of "the medallions were supposed to be able to be equipped in OoT, but that idea was scrapped."
But the question I have is, couldn't Ura Zelda have just been the extra stuff that they cut out of the original OoT? This is just my hunch on the subject, but it would explain basically all of the arguments for new items, new characters, new quests, etc. It could also explain why Nintendo decided not to even release it: like, maybe a divided development staff on the content. That would explain why items, characters and quests were excluded from the final release of OoT. Even if they finished it, someone somewhere decided against its release and the idea was canned.
Now, it was mentioned earlier on this thread that at one point Majora's Mask and Ura Zelda were mentioned as separate games entirely. I still stand by my theory (based on just the things mentioned in this thread) that Ura Zelda was the content cut from the original OoT and that over time, the hype for Ura Zelda from the Nintendo Team switched to promote Majora's Mask, so they just decided to can the idea before it was even released
Don't quote me on any of that, it's all pure speculation. =)