To make a new kernel:

cd /usr/src/linux
copy the .config file someplace
make mrproper
make xconfig (the graphical X11 kernel configurator)
 do your stuff here- you can load previously saved set of stuff 
 and just change from there
make dep ; make clean
make boot
make modules
rm -rf /lib/modules/2.0.27.old (or copy them)
mv /lib/modules/2.0.27 /lib/modules/2.0.27-old
make modules_install
cd /boot
backup your old kernel (mv vmlinuz-2.0.27 vmlinuz.old)
cp /usr/src/linux/arch/i386/boot/zImage vmlinuz-2.0.27
edit lilo.conf to have option to boot old kernel
lilo

reboot and test away
(somewhere make a floppy boot disk, too)