2010.01.06
This is code straight from the LKMPG for Linux 2.4 kernel.
Works on the Slackware2.4 handout kernel vdi in virtualbox.

  make                     to compile
  lsmod                    to see the currently loaded modules
  insmod ./hellomod.o      to inser the hello module
  lsmod                    to see the newly loaded hellomod module
  tail /var/log/syslog     to see the kernel print messages that got
                             printed upon hello module loading.
  rmmod hellomod           unload the hello module.
  tail /var/log/syslog     to see the kernel print messages that got
                             printed upon hello module loading.
  lsmod                    to see currently loaded modules
     

2009.07.23
I got this now to work on this Linux 2.4 kernel except the
KERN_ALERTs do not show up on the console, just in /var/log/syslog.

I had to do the following to get it to compile.
  add the -c option which makes the compiler not look for main.
  add the ifndefs to get rid of redefinition warnings for __KERNEL__
    and MODULE