Here' the script I use to add a network (sk98lin)
driver to a 304 kickstart CD.  SHould be the same
for a straight boot CD, AFAIK.
-------------------------------------------------------------
#!/bin/bash
SRC=/SL/3.0.4/i386/Extras
SK98LIN=$SRC/Drivers/Network/sk98lin.o
BOOT=2.4.21-27.0.2.ELBOOT

mkdir /tmp/newcd
cp -r /mnt/cdrom/* /tmp/newcd
cd /tmp
chmod -R u+w newcd 
rm newcd/isolinux/boot.cat

cd /tmp
gunzip -c newcd/isolinux/initrd.img > initrd.img
mkdir /tmp/loop
mount -o loop initrd.img loop

cd /tmp
gunzip -c loop/modules/modules.cgz | cpio -dvi

#++ Copy modules into dir

cd $BOOT
cp $SK98LIN i386/

cd /tmp
find $BOOT
gzip -c modules.cpio > loop/modules/modules.cgz

#++ Now edit module-info

cat >> module-info <<__EOD__
sk98lin
	eth
	"Marvell Yukon 88E8053 Gigabit Ethernet Controller"
__EOD__

cat >> module-info <<__EOD__
0x11ab	0x4362	"sk98lin"	"Marvell Technology Group Ltd. Gigabit Ethernet Controller"
__EOD__

cd /tmp
umount initrd.img
gzip -c initrd.img > newcd/isolinux/initrd.img

#++ Now burn the CDROM

cd /tmp
mkisofs -o newcd.iso -R -J -l -r -V "Kickstarter" -b isolinux/isolinux.bin \
	-c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table newcd/