Sounds on the Internet are currently not as popular as pictures for example. Why ?
Because of the:

• Size of files. Sounds can be very large files, even if the sound is relatively short (less than a minute) On a slow network connection (such as modem lines), they can take a very long time to dowload. Also, large files require a big space storage in order to play and many player programs require that the entire sound be able to fit into the physical memory at one time.
• Lack of hardware. Many computer systems, especially older ones, do not have sound capabilities. On many PC and unix systems, sound capabilities are not integrated into the main hardware, and are therefore an extra expense for which many businesses and schools are not willing to pay.
• Difficult to use. Many of the commonly used browsers do not have internal audio playing capabilities, which requires effort to set up sounds to play on that paricular machine.

But in the near future with the development of the multimedia computers, sound will become an important issue. Moreover, the development of telephony and radio broadcasting over the Internet will attract a lot of people.

The sound on the Internet is still at its first step ... Wait 1 or 2 years and you'll see :) MP3 format is slowly coming ...