Booting DOS from a USB thumbdrive
first, fdisk the drive, create a primary partition that is 32M, make it bootable and type fat16 (type 06)
next, install dosemu. edit your ~/.dosemurc to include the line:
$_hdimage = "drives/c drives/d /dev/sdc1"
then edit ~/dosemu/drive_c/autoexec.bat and comment out (add a rem) the following line:
lredir e: linux\fs/media/cdrom c
(otherwise it sees the last disk in hdimage as a cdrom drive)
now run dosemu
and from within dosemu, format /s (like the old days)
Z: format /s E: exitemu
(you must first go to the Z drive because otherwise the sys program doesn't have the correct path for command.com and friends)
once you are back in linux, you need to run
(of course, sdc is whatever your usb drive shows up as)
from here, you can mount it as a normal thumbdrive within Linux, add whatever you need (the only reason I do this is to flash my bios) unmount, and the thing should boot just fine.
Honestly, I'm not sure if the size was critical or if the install-mbr step was critical, but I spent a lot of time screwing with it in an attempt to flash my new tyan board, so I thought I'd document the steps that worked. It is possible that some of these steps are unnecessary, but when done in this order, they are sufficient.