kernel-source and kernel-header?

[lianliming <lianliming@realss.com>]

Hi all,
     i want to compile and install a new kernel. Using aptitude to search the 
"kernel" package, i find there are "kernel-source" and "kernel-header" 
packages.
    Should i install the both kernel "source" and "header" to install the new 
kernel?
    Another interesting question: if i install "kernel-source-2.6.8" and at 
the same time "kernel-header-2.6.7", what will happen?