I too have this problem, and I would bet any money that *anyone* with fc5 (and with the problematic kernels i guess) have the this same problem.
It would be nice to get a sticky for this just as the gfx card issue recieved. WE may not have a solution for the nforce drivers just yet, but at least people will be able to easily see that there are other experiencing the same problems.
It is quite difficult to find any information about people having problems with the nforce drivers, obviously because a lot less people use them compared to the nvidia gfx driver.
Anyway enough of that.
I guess the nforce driver is suffering a similar problem to the gfx driver (that is purely a guess, as I am basically a linux noob). What I cannot understand is that the ethernet driver installs ok (NOTE only after updating the kernel) but the audio driver still fails to install.
For completeness I will attach my install.log. But I would like to see a nvidia representative sticky this, as we have three different people all suffering the same fate, and see if we can't find some solutions to the problem