It turns out that a system migration to a new hard drive on a different drive controller resulted in the windows kernel booting from one location, but the boot file listed it on the old drive. So the update would install and link the kernel back to the old drive instead of where it should have been, and boom instantly unlinked boot sequence. This happened with any update that changed the kernel.
I attempted to do a complete reinstall from the original windows home cd, but it was so old it didn't have the required SATA support even with the required sata and raid drivers added in during installation. So I used a spare winXP pro license I has acquired for emergencies like this, and the re-install worked like a champ. Computer works fine, and I got almost everything I need/want/use from my backups and archives so it's actually a bit better now than it was.