Okay, boys and girls. As stated above, on many occasions, I found links to specs/jumper settings/other docs relative to my dual floppy drive - but all the links were 10 to 20 years old, and are now obsolete. In sheer desperation, I kept modifying my search terms slightly, until, believe it or not, i came up with a still-valid link to the jumper settings for this bad boy. I set the jumpers to identify Drive A as 5.25", and Drive B (the BIOS has no provision for Drive B, but I don't care) as 3.5".
Now I can copy all the contents of my 20-25 year old floppy disks (there are a ton of them - I used to do a lot of programming) to a spare hard drive I set up in the Dell 4400, and I have 35 gb of space for it, instead of about 1 gb on the old DOS machine which originally housed the dual floppy drive. When I get everything transferred to the hard drive, I'll make permanent copies on either 3.5" floppies, or CDs, or both.
Thanks so much to all of you on this forum for your invaluable suggestions and technical advice, especially Computer Commando and BC Programmer. Computer Hope really rocks!