The Inquirer publishes article, where noticed Matsushita's driver, which allows to work with external USB disks under DOS. Example of config.sys and autoexec.bat to access external CD-ROM:
config.sysDOS=HIGH,UMB lastdrive=Z device=HIMEM.SYS devicehigh=USBASPI.SYS /v /w /e devicehigh=DI1000DD.SYS devicehigh=USBCD.SYS /d:USBCD001
autoexec.batLH MSCDEX /d:USBCD001
usbaspi.sys and usbcd.sys available at: http://panasonic.co.jp/pcc/products/drive/cdrrw/kxlrw40an/driver/kxlrw40an.exe
di1000dd.sys available at: http://www.stefan2000.com/darkehorse/PC/DOS/Drivers/USB/mhairu.zip
Original The Inquirer arcticle and translation to Russian available at: http://theinquirer.net/?article=10215 and http://www.compulenta.ru/2003/7/8/40353/.
Yes, I tested that on a couple of machines and it is very neat to be able to access your USB flash drive on (Free)Dos. However on some occasions I experienced lockups in the ASPI Storage block device driver (DI1000DD.SYS).
Here is the most detailed installation info (or references to that) on USB for Dos solutions I could find thusfar since the original stuff is very Japanese. http://www.computing.net/dos/wwwboard/forum/13447.html
Henk van de Kamer adds:
I found the Cypress USB Stack driver for DOS (http://www.pocketec.net/downloads/duse_4_4.zip). In FreeDOS (kernel.sys 2032a and command.com 0.82 pl 2) it raises a kernel panic. In DOS 7.x (from Windows 9x) its seems to load correctly, but afterwards any access to drives raises a can't read error.
In various newsgroups it is suggested that it will only work if you can boot from USB mass storage, which my old computer can't. Piy, because it would be nice to have read/write access to storage sticks on a DOS rescue system.