This was a far more informed posting than mine. Correct, I'm running 64-bit FC6 perfectly with on-board sound. However Mauriat has reminded me that I am running 32-bit Firefox so that is the main issue it seems for people. Xine/mplayer/vlc though have not let me down..
I'm not saying which version to use, but most likely your sound will be fixed by either (manually) upgrading ALSA or the kernel. However it probably is more practical to upgrade Fedora as mentioned. But there's always a chance that even an updated FC6 may have sound card issues.
An added note. If you are interested in multimedia, 64-bit linux does have some limitations. Certain things like web browser plugins and using some 32-bit windows codecs may require some extra work to setup.