|OK, got it fixed! Whatta mess!|
Apparently early in my attempts to go back from NTFS to FAT32 I used (or misused) SwissKnife or one of a few other utilities and somehow caused the creation of 4 partitions ("volumes"?---I'm still trying to figure out the language of partitioning) on my drive. That drive is a Western Digital WD10EAVS packaged by Fantom Drives as its USB "Green Drive."
So whenever I tried to re-format it, only the ~800 GB partition was "seen" and formatted, which accounts for my lost 100 GB.
Working between Windows XP and Vista on my two computers I finally realized this (using the Disk Mgmt tool) and was finally able to create a single, unallocated partition, and then apply the wonderful fat32format.exe utility!
So now I've got the full 1 TB drive in Fat32, as needed by my DVD player. And that player, though it disclaims compatibility with USB hard drives (it claims only thumbdrive compatibility) can see it all!
The DVD player is a Philips 5990/37 and I am highly pleased with it. Most of what I want to play has been compressed to under 4 GB, so that FAT32 limitation is not a problem for me.
I thank you all for your generous help and encouragement!