The topic of the Voyager golden records always brings up some interesting and imaginative comments. I think it's pretty darn cool.
Really, I think the odds of it ever being found by someone other than us are vanishingly small. Neither Voyager will reach another star for thousands of years, and radio searches have been made in their directions of travel found nothing (as expected). In the end, it's a PR stunt and an academic exercise, but it's a fun one. Or as JohnD said, it's Sagan being romantic.
Interestingly, they essentially did send along a phonograph for an advanced civilization to play it on. Probably more useful in fact. Here's a graphic explaining the heiroglyphs on the front cover:
http://upload.wikimedia.org/wikipedia/c ... rCover.jpg
In addition to a very fundamentally-derived instructions for a phonograph, NASA included a phonograph needle on the spacecraft.
Imagine NASA finding something like this in space. After establishing that it really was extra-terrestrial, they'd be pretty careful to study it in detail as non-destructively as possible. The golden record would stand out because engineers would quickly recognize that it serves no discernible purpose. Because of our vast usage of time-based signals, once we realized there was a deliberately cut groove in the disc it would be obvious it contained some kind of signal. Any civillization that communicates in a remotely similar way should be able to realize the same. From there it would take a bit of ingenuity to figure out what it was.
Presumably, someone would be smart enough to recognize the included phonograph needle as an instrument for measuring the profile of the grooves. The drawing of the needle on the cover provides a link between it and the information there. After building their own reading device, the next big challenge is getting the timing right.
The hydrogen atom illustration gives the timing, but I'm not sure, even with the consistent use of the binary markings, that the link between the atom and the timing is obvious, or even that the lower right illustration represents hydrogen atoms.
However, one of the data images stored on the disc is a circle. I think the odds would be pretty good that looking at the signal, some confused scientist would notice the nearly regular spacing of signal peaks. That sets the stage for discovering the spacing of those peaks is definied by the chord length of a circle at regular intervals...which would be hard to interpret as coincidence. In this way you could independently determine the rate to turn the record.
From there, the rest of the images should be obvious, but I don't know if the audio recordings would be. Someone would have to recognize that their sound levels rather than image data. And the written information, in a completely foreign language, would also be a kind of Rosetta Stone.
Finding earth from this requires having already figured out the timing (and the link between that and the hydrogen time-unit). From there, we'd have to recognize that frequencies were pulsars. I think it'd take a stroke of pure brilliance to recognize that, but if someone did, it would be obvious from the drawing that the spatial orientation of those pulsars was something of significance.
Here's a really interesting page with the contents of the record, including the images and wav files of the sounds:
http://re-lab.net/welcome/
