What will work to make an image of a bootable HFS format Zip 100 disk in Windows? I want to be able to mount the image as a drive for Basilisk II.

You might give HFVExplorer or MacDrive a go...
Another tool that I haven't tried, but might work for you could be HFSExplorer.

They're all on Google, so you'll be able to find them (by name) with very little trouble.

Whether you'll be able to use the resulting disk image as a bootable drive in BII (basilisk II), well, I wouldn't know. But at least you'd get access to your files.

The easiest way might be to create the image with the MacOS.
Besides that you might try ImgBurn http://www.imgburn.com/ or AnyToISO http://www.crystalidea.com/anytoiso.
Good luck!

Well crap. I was able to mount the ZIP 100 disk in old Basilisk II 142 but HFVExplorer wouldn't see it (or any of my other old ZIP disks) as Mac disks.

The drive I'm using is a USB powered Zip 250, recently picked up for free, so I decided it's time to copy my old stuff of the old disks. I have it selected in the GUI as a "floppy". (Where, oh where is that option in the GUI for the JIT builds and SheepShaver?)

Disk First Aid claims they aren't HFS disks. Really? Then how does OS 8.1 mount and read and write them?

Well now one of them's got something kablooie on it somewhere so that OS 8.1 isn't seeing it as being formatted. It's claiming it's a blank or unsupported format 1.44M floppy and it must be initialized or ejected.

How do I keep the disk in the drive so I can try running some recovery utilities on it? I don't recall how/what I did with real Macs! That was always the most annoying thing about the Mac. It was not easy to make them keep sick disks in removable drives so they could be worked on.

Well it's Windows to the rescue! I used TestDisk to extract an image of the HFS partition from the Zip disk.

Then I renamed image.dd to image.hfv and selected it in the Basilisk II GUI. Booted up and Mac wants to initialize and I click Cancel.

Disk First Aid fixes a b-tree problem and the disk mounts. I have Norton Utilities on the Zip so I copy it over to the image Basilisk is booted from and run Disk Doctor on the Zip image, which fixes some more errors.

So now I should be able to format the disk as a FAT volume in Windows, then Erase it to HFS in Basilisk.

I love this utility, saved me big headaches a few times. http://www.cgsecurity.org/wiki/TestDisk_Download DOS, Windows, Linux and OS X versions.

Good to hear you made it! Thanks for the link to TestDisk, I will sure give that a try.
I had my SCSI MO and a hard disk connected to build 142 some time ago. They worked fine, as long as it was HFS and not HFS+, of course.
Some GNU-Linux distros are supposed to read / write HFS and read HFS+, but it is better to have different solutions at hand.
I still have my old Macs, so I am lucky to be able creating images with DiskCopy or Toast.