Thanks for the responses! Since my original post, I've managed to cure some of my ignorance, and also accomplish my original goal, which was to extract my mom's email address book from the Sandisk. I'll give you the rundown on how I did that, but I guess that's really off-topic from the QEMU question, so first about QEMU...
QEMU docs say it automatically figures out geometry of disk images, but it has an option to specify geometry: -hdachs c,h,s[,t] so I tried it like this: -hdachs 490,2,32 and that gave the same result, the failure to access /dev/hd0t77. Same thing when I give auto or none for the optional part at the end, the translation mode. However, when I saw Wild-pencil's comment about lba, I also tried lba. It worked less well, I think, the emulator started chewing cpu cycles, but did not get past Booting from Hard Disk. Does the iOpener's Sandisk use lba mode? I always assumed it was normal mode.
By the way, I figured out what the "t77" in hd0t77 means. I believe it means file system type 77, or QNX-4 format.
My next step was to explore running QNX in QEMU, and I ended up downloading the CD image for QNX 6.1 and installing it in QEMU, and that worked great. Next I tried giving the Sandisk image file to QEMU as the second disk image, and booting into QNX, and that also worked great, QNX automatically mounted the QNX-formatted partitions from the Sandisk image into three directories in /fs.
The rest of my story is about QNX, so maybe it's not interesting to folks on linux-haker, but here it is anyway. This installer for QNX 6.1 really made things easy for me. After having good luck with it in QEMU, I next installed it onto a laptop hard drive and tried to boot the iOpener with it. This did not work, QNX hung early in the boot process. I had good luck with Windows 98 on my previous iOpener, and the QNX installer has an interesting option where you can install it to a file under Windows, and that file holds the entire QNX space, and when Windows is booting, QNX will swap itself in and take over. A dual boot system of their own invention. So I installed Windows 98 onto the hard drive, copied the QNX installer to the hard drive, booted the iOpener into Windows 98 (I already knew how to do this). Then I ran the QNX installer, installed QNX to file, and rebooted. Magically, the iOpener booted up into QNX from the hard drive.
As it did in the emulator, QNX automatically mounted the partitions from the Sandisk into /fs, so I was able to browse them, and in about 5 minutes I found the email address book. The partition was mounted in /fs/hd1-qnx4, and the file was .../dsm/<ten digit number>_addressbook.acap. I need to ask about dsm and the acap file format, which I'll do in a separate thread. Remember the hard drive is formatted DOS, and the QNX space is inside a file on this DOS drive. QNX also had mounted the "host" DOS file system in /fs, so I was able to cp this file out there, switch the hard drive to another computer and retrieve the file. Ta da!
So that was my goal accomplished, but I still want to play out the emulation question as far as I can. So the next thing I did was to boot the iOpener in Windows again and use Dolly to copy the Sandisk image to a file. So now I have my mom's Sandisk image to compare with the pristine v2 image. While I was at it, I also used cp -R to copy the contents of the QNX partitions into the DOS space, as a form of backup, but in the process, cp failed on a currupt file: np-misc.fs. Hmmm, could this corrupt file be the problem the brought down the iOpener? Can I replace this file with the same file from the v2 image and get the iOpener working again as an email machine? We shall see. First I have to figure out how to use QEMU to get the good np-misc.fs out of the v2 image. To do that, I need networking to work between the QEMU machine and the host machine, and I haven't gotten that going yet. That's next.
I tried one more time to boot the iOpener disk image using QEMU, this time using the file I'd just made with Dolly from my mom's iOpener. Interestingly, it boots very much like it does on the real machine, until it once again complains it cannot access /dev/hd0t77. I'll follow this post with a screenshot.
Regarding Linuxguru's post, so far I've not using Linux to do anything, I've done my disk image copying with Windows and Dolly. Would I get better results if I used Linux and dd?
I'm not too surprised that QEMU will not boot the iOpener Sandisk image. Early on in my experiments, I had zapped the v2 Sandisk image to the hard drive using Dolly, and after I did that, my PC would no longer boot with the hard drive attached. I couldn't even boot from floppy or CD with this hard drive simply attached. Something in that disk image is incompatible with the (old) BIOS of my PC. So I'm not surprised that the BIOS of the QEMU emulator has trouble with it as well. I wonder what it is. I'm out of ideas for getting it booted in QEMU, but I'll add some more to the thread when I figure out QEMU networking and get the np-misc.fs file out of the image.