It is possible to install a dualboot between FreeDOS and Windows.

MS-dos, Windows 95/98/98SE/ME (Millennium Edition):

*have your Microsoft operating system installed.
*install FreeDOS. do NOT issue the command called BOOT.
*save the Microsoft Bootsector by running SAVEBS-C.
 This creates the file bootsect.bin
*create the file c:\fdos.bin :
 SYS C: C: C:\FDOS.BIN BOOTONLY

*rename the file C:\KERNEL.SYS to C:\FDKERNEL.SYS.
This is the FreeDOS kernel (core, nucleus),
REN C:\KERNEL.SYS FDKERNEL.SYS

*copy a:\kernel.sys to c:\kernel.sys
This is a file of 2KB, consisting of Eric Auer's MetaKern bootloader.
By default it can only load FreeDOS.

*add the saved bootsect.bin to kernel.sys:
COPY /B C:\KERNEL.SYS + BOOTSECT.BIN C:\TEMP.SYS
DEL C:\KERNEL.SYS
REN C:\TEMP.SYS KERNEL.SYS

*write the bootsector to C:
SYS C: C: BOOTONLY


Windows NT/2000/XP:

*C: needs to be FAT or FAT32, not NTFS or Dynamic Disk
*install FreeDOS to c:\fdos for example.
*add a line to c:\boot.ini:
 echo C:\FREEDOS.BIN = load FreeDOS beta9 >> c:\boot.ini

*write FreeDOS bootsector to c:\freedos.bin:
 SYS C: C: C:\FREEDOS.BIN

* now the NT bootmenu displays the option to load FreeDOS.