Upgrading kernel used in PXE boot

[Eric Smith]

I'm installing FC6 using kickstart from PXE.  It works great, and I've 
used this (and a similar setup with FC2) for years.

Now, I want to use a new kernel during the installation.  FC6 comes with 
  2.6.18-1.2798.fc6, and I want the boot to use some version of 2.6.20 
or greater.

What I've been doing is installing with the default kernel, then 
upgrading to 2.6.20-1.2962.fc6 after the installation is complete.  But 
now I have a need to run 2.6.20 during installation, because of some 
hardware that's supported in 2.6.20 but not in 2.6.18.

So my question is:  How do I create a new initrd.img and vmlinuz (that 
came in the isolinux directory) to be a new kernel?  It's apparently not 
as simple as copying these files from a running system.

I've spent hours googling.  I've seen all sorts of info on adding 
drivers to initrd.img, but no info on updating the kernel.

Any info would be great!

Thanks.
Eric.