"The only Beta ROM that was ever publicly accessible was the Zelda 64 cartridge used at the Space World convention in 1997. This cartridge allowed you to visit Link's house, tour Hyrule Field on Epona, see the castle from the outside, and take a look at a simplified version of Zora River. You could also fight two Stalfos, Ghoma, or King Dodongo, and explore three different dungeons (presumably Dodongo's Cavern, the Deku Tree, and Jabu-Jabu's Belly). There was another one on display at an E3 convention, but it was one very close to completion and had little beta material remaining."
"Sadly, neither of them are available anymore, and there was no opportunity for people to download the data off of the cartridge onto a computer. All of the beta material still exists, but it currently is stored in Nintendo's archives and is inaccessible to anyone without the proper authorization. Unless a wonderful miracle happens, this material will never be released in full form. Somewhat strange, really... think of how great of a marketing technique that'd be!"
- From the website Zelda's Secret Ocarina
It would be really cool if they made the beta Ocarina of Time downloadable for Nintendo's upcoming Revolution. It ain't gonna happen though. I think game devolopers usually don't want to show preliminary versions of their games, it's like showing an unfinished painting.