Repo error

[Ronald]

This is my kickstart file:

auth --enablemd5 --enableshadow
bootloader --location=mbr --password=blablabla
firewall --disabled
firstboot --reconfig
install --partition=sdb2 --dir=/back-up/Os/fc/
interactive
keyboard us-acentos
lang nl_NL
langsupport nl_NL
mouse --device=input/mouse0 logitech
part /mnt/shared --usepart=sdb1 --noformat --fstype=vfat
part /mnt/data --usepart=sdb2 --noformat --fstype=ext3
part / --usepart=sda5 --fstype=ext3
rootpw blablabla
selinux --disabled
xconfig --startxonboot
repo --name=extra 
--baseurl=http://download.fedora.redhat.com/pub/fedora/linux/extras/6/i386/

I'm using Fedora Core 6 and I'm trying to create a kickstart file for 
installation on multiple machines. My LAN-card works fine when I 
activate the Fedora Extra in a 'normal' installation. But I want to add 
external repository's with this kickstart (it seems that kickstart 
doesn't include Fedora Extra's by default so I try to add it), but it 
seems that:

repo --name=extra 
--baseurl=http://download.fedora.redhat.com/pub/fedora/linux/extras/6/i386/

is wrong. I don't know why, or how. The error Anaconda gives is:

"Unable to read package metadata. This may be due to a missing repodata 
directory. Please ensure that your install tree has been correctly 
generated. Cannot open / read repomd.xml for repository: extra."

Can someone help me?