Not exactly. What was being described was taking the 5.1 audio stream and extracting each of the 6 channels into single, discrete files. This is necessary because - as far as I know - there is no software that enables one to edit an AC3 file in its native form (which is understandable, as it was intended as a delivery format, not an editing format.)

There is no way to effectively separate the music, sound effects, and dialogue from any one of the 6 channels, but certain channels tend to carry more of one of the three. For example, a majority of the main dialogue will be in the center channel, with very few sound effects and almost no music. The left/right channels tend to have the most music/sound effects, and the surround channels tend to be a hodge-podge, depending on the film. For example, in Das Boot, the constant "drip, drip" of water tends to come mostly from the surrounds, to give the effect of being "in" the submarine.

If you want the music completely isolated, you are better off buying the soundtrack, or downloading the ISOMIX DVD. As to sound effects, you can download samples from:

The Soundbunker,

TheForce.net,

More sources, including the two links I just gave.