" Your comment about BIOS options, why would they have anything to do with anything?"
My comment about the BIOS was based on this line of logic:
You had a working hardware/software combination. Then you changed CPUs. Then you changed back to the original CPU which now does not work. You made no software changes during either CPU swap. The initrd error usually is caused by the kernel not being able to access the / partition. So perhaps in the process of swapping CPUs the BIOS got reset to its default values and initrd is no longer able to work because it cannot access the disk. So check your BIOS parameters to see if the disk geometries are still correct in the BIOS.
"Normally I have the first boot device set to C: drive. When I'm installing/recovering I set the bios to boot either;
CD-ROM then Floppy, then C:
Floppy then CD-ROM, then C:
some other combination (LS120's, Zipdisks, etc.) It's a rather flexible bios.
When I am finished I reset it to boot from the C: drive only."
This is reasonable. But as a test try setting the BIOS to exactly the way that you used to run under normal conditions.
"Are you saying that LILO/Linux/or some combination thereof won't let me boot into Slackware 9.1 if the boot options are different from when I installed it?"
In my reply I assumed that you made no changes to the LILO software at all. If you did then try booting a rescue CD (I think that the Slackware install CD has one, but I'm not sure), using the rescue CD to boot into Slackwre, and then repairing LILO.
"Seems like one heck f a security risk."
Anyone who has physical access to your computer can get into your computer with a boot floppy or boot CD. The boot CD does not even have to be the same OS as your system as long as the boot CD has the logic to access your file systems. The only logic block to bootable CD's is to have a hardware password.
Be prepared. Create a LifeBoat CD.