[CentOS] Kernel source - linux -2.6.18 i386 or i686

As I plow through the Kernel source to figure out why the BEET patch is 
not working, I notice that there are two similar directories under 
~/rpmbuild/BUILD/kernel-2.6.18:

linux-2.16.18.i386 and linux-2.16.18.i686

So which one am I suppose to be patching?

Currently, the patch starts out with:

diff -urN  a/net/ipv4/xfrm4_input.c b/net/ipv4/xfrm4_input.c

I followed the kernel source setup instructions on the wiki: 

http://wiki.centos.org/HowTos/I_need_the_Kernel_Source

tells me to supply i686 for getting and setting up the source.

But http://wiki.centos.org/HowTos/Custom_Kernel

has me setting up a .config file with '# i386' as the first line.  Now 
that is a comment, right? So why add such a comment.  Perhaps it is NOT 
a comment?  Shesh...

Anyway, which directory structure gets used in the rpmbuild:

rpmbuild -bb --target=`uname -m` kernel-2.6.spec 2> build-err.log | tee 
build-out.log

Do I add this to the patch?