sound gone on feisty

Please follow the help and advice of this page when debugging/asking support on sound issues:

https://help.ubuntu.com/community/DebuggingSoundProblems

Let me also warn you that unless you really know what you are doing (and even then) installing third-parties drivers may be more harmful than beneficial to your system.
Beside, ubuntu officially cannot give you any support when these drivers/software are installed (or fails).

Okay, so the realtek drivers are a bad idea then.

I read that debugging page, but I'm not really sure where to go from there. I saved all the output from the commands it said to run. The page says to run modprobe and a module name.
Where do I get the module name?

Here's the sound card I have on the alsa page that help page linked to: http://www.alsa-project.org/alsa-doc/index.php?vendor=vendor-Nvidia#matrix

First of all, let's see if you have modified any runtime configuration files that affect how alsa-lib interacts with your sound devices. Can you tell us what is the output of the command:

cat /etc/asound.conf ~/.asoundrc*

I assume you have uninstalled the realtek drivers, if not please do so before continuing.

I haven't uninstalled them, but I'm not sure if they were installed in the first place.
What would I need to do to check to see if they're installed and then uninstall them?

right now that command returns:
cat: /etc/asound.conf: No such file or directory
cat: /home/cameron/.asoundrc*: No such file or directory

>What would I need to do to check to see if they're installed and then uninstall them?

How would I know?
I guess (and it really is a guess) you should go to the directory which contains the files you downloaded (the files not the compressed archive) and try with a "make uninstall" command.
Or perhaps there is an option in the "install" script you used.
Check the README, INSTALLATION or any similar files which were included in your download as well.

okay, make uninstall says it worked.

cat /etc/asound.conf ~/.asoundrc* still returns this:
cat: /etc/asound.conf: No such file or directory
cat: /home/cameron/.asoundrc*: No such file or directory

Look, this is the beginning of the install script you used:

echo "Remove old sound driver"
if [ -d /lib/modules/$KERNEL_VER/kernel/sound ]; then
   rm -rf /lib/modules/$KERNEL_VER/kernel/sound/pci > /dev/null 2>&1
   rm -rf /lib/modules/$KERNEL_VER/kernel/sound/acore > /dev/null 2>&1
   rm -rf /lib/modules/$KERNEL_VER/kernel/sound/driver > /dev/null 2>&1
fi

With the above lines you have deleted all ubuntu kernel modules related to sound.

## remove driver modules
if [ -f /etc/rc.d/init.d/alsasound ]; then
   /etc/init.d/alsasound stop
   rmmod snd-page-alloc > /dev/null 2>&1
   rmmod soundcore > /dev/null 2>&1
fi

And with these you have uninstallated the two core modules.

echo "Remove old alsa library"
rm -rf /lib/libasound.* > /dev/null 2>&1
rm -rf /lib64/libasound.* > /dev/null 2>&1
rm -rf /usr/lib/libasound.* > /dev/null 2>&1
rm -rf /usr/lib64/libasound.* > /dev/null 2>&1

With these you just deleted all the ubuntu sound libraries.

Later on the script replaces them with its own version + its own alsa-lib and alsa-utils,

In a nutshell, unless you want to manually try to undo all this, you have to reinstall 7.04 from scratch.

Okay, if that's what it takes.

Should the fresh copy of feisty support my sound card?

It better will. The AC 97 must be the most common sound chip on this planet.

Okay, time to make lots of backups then

Well, as long as you don't backup the problematic files ;-)

I'm not sure if this is a good fix or not, but I decided that if I was going to re-install ubuntu from scratch then it couldn't hurt to play with the packages and make a final attempt at fixing my current install
I opened the package manager and re-installed anything that started with "linux" or "alsa" and now my sound works fine.
Is that a good fix?

In principle yes, you reinstalled the whole kernel and the alsa packages (utilities, drivers, etc.).
You may have problems perhaps with OSS but as long as you don't use it (and I don't see why you should) you should be right to go.