As it happens, I finally upgarded to an Abit NV7-133R a couple of weeks ago, and got the Linux drivers installed under RH7.3this weekend. At this point, I am up and running with the nVidia drivers.
Have you installed the sound module?
When you have completed the "make install", you can manually load the module using "modprobe nvaudio". Once you do this, try to play some a sound file or .mp3.
You proabably can and should ignore the error concerning /dev/mixer. If my memory servers me, this is a MIDI device. Though I haven't had a chance to check yet, I would bet that the nForce does not yet support MIDI under linux. If this is the case, they are not much different than anyone else; last time I check, the Creative cards didn't either. (Really, neither card has hardware support for MIDI; the windows drivers for both include a software synthesizer.)
There are more things to look at later, but this is a good start.
(NOTE: The "make modules_install" for the kernel clears out the prior set of modules, so you need to restore the nVidia models each time you refresh the modules included with the kernel.)