Google search lead me to this webpage:
http://www.centos.org/docs/5/html/In...S/ch06s04.html
Here's the section regarding sound:
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6.4.8. Problems with Sound Configuration
If, for some reason, you do not hear sound and know that you do have a sound card installed, you can run the Sound Card Configuration Tool (system-config-soundcard) utility.
To use the Sound Card Configuration Tool, choose Main Menu => System => Administration => Soundcard Detection in GNOME, or Main Menu => Administration => Soundcard Detection in KDE. A small text box pops up prompting you for your root password.
You can also type the system-config-soundcard command at a shell prompt to launch the Sound Card Configuration Tool. If you are not root, it prompts you for the root password to continue.
If the Sound Card Configuration Tool does not work (if the sample does not play and you still do not have audio sounds), it is likely that your sound card is not yet supported in Red Hat Enterprise Linux.
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Hope this helps