Thank you, Werner.

I did some more searching and testing, resulting in a bootable flash drive.

First test was to use the Knoppix Flash Installer again ("p" option) and note the characteristics of the install. Knoppix (CD boot) Gparted said that there was an MSDOS partition table, /dev/sdc1 was 904 MB FAT32, /dev/sdc2 was 6.58 GB resiserfs. Result was unbootable on Dell.

I then booted Windows Vista. Looking at the flash drive, I noted that there was /boot/isolinux directory created by the Knoppix (CD boot) Flash Installer!

Using pendrivelinux.com Universal USB installer tool, I specified the distro as Knoppix and pointed to my Knoppix .iso file. I chose the "format" option for a new FAT32 format. It wrote the first partition, but ignored the second partition. The resulting partitions appeared identical to those created by the Knoppix Flash Installer, but with one important distinction -- /boot/syslinux instead of /boot/isolinux (as done by the Knoppix Flash Installer). The result was a bootable flash drive, recognized by the Dell BIOS as USB-HDD0.

A few minor points --
Acer was also happy to boot the new flash drive

The Dell docs say boot devices should be plugged into front panel USB. Both front & rear worked fine.

Knoppix (flash boot) Gparted saw the same partition info on the Pendrive Universal Installer flash drive as reported after the Knoppix Flash Installer. Difference appears to be contents of the /boot directory, as created by the two different installers.

There was a boot prompt that indicated that no file had been specified for saving personal information, but that could be specified later. Bypassed it and used the system.