Sometimes you need to build additional kernel modules, for example the get your nvidia card working or to build the alsa modules. But these can only be compiled if you have the kernel sources, and you need them configured exactally like the kernel you are running. For this you will need the .config file in the kernel source directory, but with most distro's this file is non existant. I you just configure the kernel sources according to your whishes, you will get modules errors when you try to insert your new modules.
Other then installing a new self compiled kernel and then installing the modules, how do you get around this?

I don't know about other distros, but RH ships the config files used with the kernel source files (it's under /usr/src/linux-2.4/configs IIRC -- I am on windoze now). There you will find configs for athlon, SMP etc.

The trick is to run 'make mrproper' after copying the desired config file to .config on /usr/src/linux-2.4. (it took me too many failed attempts to figure that out...). I am not sure this is really needed, but 'make oldconfig' right afterwards should do more good than bad. After these, go for kernel-options tweaking.

HTH

Correct me if I'm wrong, but if I look in /boot, there are kernel config file(s). I've always assumed these are associated with the pre-compiled kernels that ship with the distro. try copying to your build directory and go from there.