The driver FC4 supplied by default worked fine, but for some reason I went ahead and installed the proprietary ones from Nvidia. While my audio still works, volume control features on programs like XMMS no longer work. I have to adjust audio from the speaker icon on the upper right of the screen. I also noticed upon rebooting that I get a FAILED message as Fedora is closing itself down. It says something like ALSA device not found or something like that.

What is the advantage of using the nvidia driver? If there is no advantage at all, how exactly do I revert to the original driver installed by FC4?

./NF* -uninstall

You should install the nforce drivers at init 3 and make sure your kernel source is installed. You will need to re-setup your sound card. I haven't used fedora in a year or so, but if the setup command is still there you should rerun it to remap your "new" sound card that is detected.