Let's see if I can tackle this for ya:
/lib/modules/newkernel will have any modules you created during make menuconfig. If the module for your sound card isn't there, you likely left it out, or compiled it into the kernel. Since you are getting the /dev/dsp deal, I'm guessing you left it out
The FrameBuffer is what enables Tux at the top of the loading console. That is in the FrameBuffer section, and if you get a new enough kernel it even says "cool tux thingie" or something like that as the option
If kernelversion and newkernel are the same, you really wanna look at moving the old kernel modules to an 'old' file, like so:
mv /lib/modules/kernelversion /lib/modules/kernelversion.old
And then the new one won't overwrite the working/old one. That's only if they are of the same release (2.4.20 and 2.4.20).
You should have also copied over System.map from the bottom part of the kernel tree (assuming /usr/src was where you compiled it would be:
/usr/src/linux-2.4.21/System.map also assuming 2.4.21

) to /boot I do that and copy it to something like:
cp /usr/src/linux-2.4.21/System.map /boot/System.map-2.4.21
And then make a Symlink so I don't overwrite the old one (that is also symlinked):
ln -sf /boot/System.map-2.4.21 /boot/System.map
HTH
Cool