sory for old thread , please try this
a bit different variant of freedos (it is called balder)
http://www.finnix.org/Balderit has FDXMS (replacement for himem&emm386)
safe mode usualy just works.
loadcd.bat loads cdrom drivers on the fly
usb memory may be detected as A: or B: when booted using motherboards usb boot
this is usualy if mobo has recognised usb memory as USB ZIP
may be slow, on other hand may have RW capabilities to usb.
EDIT
i think XMS memory managers from DOS may be having conflicts
in combination to PloP's usb driver (not allways)
(sometimes the content of usb stick is garbled when chosen this option himem or emm386 or fdxms)
FDXMS appears to allocates 1 GB to 4GB of RAM to be used from inside DOS , i found it unbelievable

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