To run a kickstart installation for RHEL6, boot as usual. At the window “Welcome to Red Hat Enterprise Linux 6.0”, select “Install or upgrade an existing system”. Press the tab key to stop the boot process. You should be presented with a prompt that looks like this:

> vmlinuz initrd=initrd.img

Add your kickstart information to the end of this prompt. So, it should look something like this:

> vmlinuz initrd=initrd.img linux ks=http://rhel6.example.com/ks/cfg/org/24/label/kickstart_file 
ip=192.168.4.45 
netmask=255.255.255.0 
gateway=192.168.4.1 
dns=192.168.5.14

(all on one line)