You can install every package that you need with Synaptic.Just search for "kernel".It will install all kernel related packages in /usr/src.
Here's a list of the directories in my /usr/src at the moment;
kernel-patches,linux-headers-2.6.24-1-486,linux-headers-2.6.24-1-common,linux-kbuild-2.6.24,linux-support-2.6.24-1,linux-source-2.6.24.tar.bz2.
Remember to select right architecture for the packages you will select.Always use compiler with wich your kernel was compiled when you're patching it,sometimes you'll need to change a environment variable for that if you have more than one compiler in your system.Here's the list of extra packages that I'll suggest you to install;kerneloops,linux-tree-2.6.24 and module-init-tools besides some already mentioned,which you need,like build-essential,etc.
Here's a good kernel-howto.