mine's working fine. be sure you to System->Preferences->Sound and make sure sound enabled is checked. mine started iwth it unchecked by devault.
I had FC5 installed for a while and was unable to get the sound to work either. After trying forever to get it installed, I gave up. Sorry i can' be more help.
I found johnb's advice -- System->Preferences->Sound and enable -- to work perfectly well. This in spite of the autoconfiguration for sound claiming that the sound hardware was not recognized (the test tones didn't come through).