They're sped up. I don't know how this effects music, however for quick voice clips, the voices sound worse than Alvin and the Chipmunks on speed and helium.
We're going to need more information in order to help. Is the problem with all your sound files, or only some? Are the sound files imported into the movie's Library, or are they loaded at runtime? Do the sound files play correctly during authoring? If the sound files are imported into the Library, do they play correctly from the Library?
Are all of the files saved to the same sampling rate? In any case, I'm guessing that the sampling rate of the files is not one that your computer is happy with. The sampling rate should be a multiple of 11025 Hz. in order to insure the best compatabilitiy. If this is the case, then you can open the original sound files in a sound editor and re-save the sound files to a more compatible sampling rate. Then you can update your sound files in the movie and see how they work.