I came up w/ an easy enough solution.
Downloaded the Ubuntu 5.04 (the hoary hedgehog) install CD.
Installed Ubuntu 5.04 without a hitch, it used the megaraid module.
Followed the instructions at this link: https://wiki.ubuntu.com/BreezyUpgrade
Installed the smp kernel, and rebooted.
My workstation booted and I'm happily setting up my Ubuntu 5.10 workstation.
BTW, it loaded the megaraid_mbox and megaraid_mm modules.
However I'm not getting the errors I was before while trying to use those modules on the Ubuntu 5.10 installation CD.
I'm guessing maybe there has been a kernel update released for ubuntu since the 5.10 release and now?