audible vocabulary database for just listening

hi
how I explain what I think....its not easy.

I need just voice/pronunciation of each word with example sentence.

yeah there are so many database/ free dictionary on internet
and I can listen to any pronunciation or example sentence with speech.
but its available only for when I search something via computer
and keyboard typing.

I don't do that when I am in out, on the train, car, walking, jogging.

I wanna listen to each word whatever whichever wherever whenever, especially it would be useful always stay word data in iPod and play them randomly.

firstly I thought I could extract each audio data as mp3 or wav files
from Dictionary DVD-ROM or English learning software.
but its definitely impossible to extract from those materials.

secondly I thought I can use vocal dictionary for blind people.
I expected blind people learn words from vocal data like what I explained above.
but truth is that no such items....

please tell me anything good idea you have.