How to prevent kernel upgrade from apt-get?

[riches@ms.washington.edu]

I am running a couple of OpenMOSIX clusters, and OM depends on kernel 
2.4.26.  I would like to use a script to run:

  apt-get upgrade

on all of the cluster members, but "apt-get upgrade" wants to upgrade the 
kernel:

  # apt-get -V upgrade
  Reading Package Lists... Done
  Building Dependency Tree... Done
  The following packages will be upgraded:
     kernel-image-2.4.27-2-386 (2.4.27-10 => 2.4.27-10sarge1)

I've tried to prevent a kernel upgrade by creating a /etc/apt/preferences 
file with these contents:

  Explanation: Prevent kernel upgrade
  Package: kernel-image
  Pin: release a=stable
  Pin-Priority: -50

but this doesn't stop the kernel upgrade.  I've tried variations on the 
package name and priority but they didn't stop the upgrade either.

After searching the mailing list archives to no avail, I must ask:

  Can someone on the list help me out with this?

Thanks,
Carl G. Riches
Software Engineer
Department of Mathematics
Box 354350                      voice:     206-543-5082 or 206-616-3636
University of Washington        fax:       206-543-0397
Seattle, WA  98195-4350         internet:  riches@ms.washington.edu