I figured it out and I'm in the process of formatting my new 80GB 1.8" HDD using the original HDD flex cable that I thought I might have damaged. The problem was "user error" (what a surprise!) as I haven't replaced a 1.8" ZIF connected drive before.
The Dell D420 manual was accurate up to the point of prying up the ZIF connector:Dismantling the hard drive
The ZIF connector on my 2 Toshiba drives is NOT the white piece. It is a thin black bar and it flips toward the near edge, NOT toward the back of the drive like the picture shows.
Steps 1 and 2, and their enlarged images, in this pictorial accurately describe the ZIF connector:Installing a Toshiba ZIF drive
As noted, when the connector is closed it lies flat and is smooth to the touch. Using a fingernail or small piece of flat plastic on the center it, pull the black strip up and back toward the near edge where the HDD flex cable was or will be inserted. It will move 90 degrees and stand wobbley and loose in a vertical position.
After the flex cable is "properly" inserted the black strip is pushed down flat to its original position and the cable is locked in place.
"Properly" is key in inserting the flex cable. In the miniaturized connector world, I did not realize when I removed the cable that it goes INSIDE the END of the white plastic piece. I was putting it under the white piece where it was loose, slid back and forth, was not clamped by the ZIF connector, and had no contacts to the HDD. DOH!
Looking straight at the end of the connector it doesn't look as if anything fits in there, but the cable does, it is the perfect width, and it makes contact. My flex cable has a white strip very near the end of the cable and this strip was still visible after inserting the cable. It is a tight fit and takes a little jiggling. I slid one end in at an angle and then slid the rest in. It only goes in a very, very, little bit, maybe a few mm's or 1/64th of an inch. The cable contacts face down, but the D420 will only go in one way to fit the cable routing. Even though it seems the cable is barely inserted, when you close the black strip ZIF connector the cable is held in place.
WHEW! Guess that's why the Geek Squad makes the big bucks, showing up perpetual noobs like me. Fortunately I didn't have to call them. I will soon have an extra flex cable that I ordered and a 1.8" external enclosure that I can use for my old 30GB drive.
Speaking of drives, if I count what is in my D420 and M1710 and immediately usable and adjacent to them (not counting the service desktop my lady uses as well as a handful of flash drives) I have a 30, 80, 80, 160, 160, 250, and 320. Hmmm. Can you say "garage sale"?