BIOS upgrade is not possible from within dosemu/dosbox or wine. Even if it writes something to the bios chip, there is a chance it might corrupt the data here - I wouldn't take the risk

I managed to create a bootable ISO, based on the N200 0867 bios update floppy image, with 3.03 bios rom.
To flash the BIOS from DOS floppy image, a quite "fresh" phlash16.exe is required. Much newer, than the one provided by lenovo for 0867.
Don't know what is the licensing of BIOS rom or the Phlash16 utility, but I uploaded my image here:
http://ft.utp.edu.pl/~madman/files/bios_cd.iso.bz2Simply unpack and burn. Then boot from the cd, and type something like:
phlash16 /c /x /s /mode=3 el10303a.rom
...and wait for Your computer to reboot.
To lenovo administrators: It would be great to create bootable ISO images of every bios release, so there is no need to manually create them for people not using Windows.