installpkg kernel-modules-2.6.18-i486-1.tgz
cd /etc/rc.d
rm rc.modules
ln -sf rc.modules-2.6.18 rc.modules
cd /usr/src
cp /diretorioondeesta/linux-2.6.18.3.tar.gz .
tar -xvzf linux-2.6.18.3.tar.gz
rm linux
ln -sf linux-2.6.18.3 linux
cd linux
make menuconfig
altera / salva / sai
make bzImage
make modules
make modules_install
cp arch/i386/bzImage /boot/vmlinuz-2.6.18.3
cp System.map /boot/System.map-2.6.18.3
cp .config /boot/config-2.6.18.3
pico /etc/lilo.conf
adciona a linha abaixo, no final do arquivo:

# Linux bootable partition config begins
image = /boot/vmlinuz-2.6.18.3
root = /dev/hdxx (hdxx a sua particao linux)
label = Linux_novo
read-only
# Linux bootable partition config ends

ctrl + o pra salvar / ctrl + x para sair
reboot