You'll find an excellent guide here
which I followed and it worked perfectly for me. As a note in the first step it says;
# apt-get install debhelper modutils kernel-package libncurses5-dev
but I suggest;
# apt-get install debhelper modutils kernel-package libncurses5-dev libc6-dev
and I also suggest reading this
Having compiled a few kernels using the Debian way I suggest that you use Debian source and not that from kernel.org. The latter does not seem to work with Debian. You may not be able to get the kernel-source for your dist through apt-get but you you can download it via your browser eg 2.4.23 you'll find here
Hope this helps.