Found this definitive answer:
http://www.winimage.com/bootpart.htm
Practical application is described
here.
Method 1:
o Copy Bootpart.exe onto the partition you will be booting NT and DOS off.
o Install DOS as per normal. Boot into DOS. Run Bootpart:
o bootpart WINNT BOOT:C: (to turn the MBR back to an NT boot sector)
o bootpart WIN98 bootsect.w98 "Windows 98" (To include a Win98 option in the NT boot menu).
Method 2:
o Boot from a DOS boot disk
o Copy the DOS directory (and IO.SYS & MSDOS.SYS) to the root of your active partition. Run Bootpart:
o bootpart REWRITEROOT:C: (to place IO.SYS and MSDOS.SYS at the beginning of the partition)
o bootpart DOS622 bootsect.622 "MS-DOS 6.22" (To include a DOS option in the NT boot menu)