I do have a way to fix the boot sector, if it gets overwritten, but
when I do, the system will no longer boot from the Linux drive.

It looks like it is trying to start GRUB from the USB drive, and then
it crashes.

I also tried PenLinux, to the USB drive, with the same effect. Which
puzzles me, because when I installed PenLinux to a flash drive, it
worked just fine. The drive is a 160GB drive. Innards are IDE going
through USB adapter. Drive is good, because I can fdisk it, and
format it to NTFS. When GRUB was in the boot sequence the USB drive
worked fine to boot into Hardy Herron.

Being a real newbie at Linux, I am at somewhat of a loss as what to do
next. I have no idea what to edit or where, but am not ready to give
up.

The nice thing about my old computer was the hard drives were all in
caddies, so could boot from whichever one was installed at the
moment.

There has got to be a way, just finding it is the trick.