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 install bootsector.
*save the Microsoft Bootsector by running COPYBS C: C:\BOOTSECT.BIN
 This creates the file bootsect.bin
*obtain from the freedos bootdisk both meta-all.sys and metaboot.bot

*Create the MetaKern bootloader entries
 (defaults to first added bootsector):
 COPY /B META-ALL.SYS + BOOTSECT.BIN + METABOOT.BOT C:\METAKERN.SYS

*Write the FreeDOS bootsector to C:, and specify 
 the name for the above created "kernel" file:
 SYS C: C: BOOTONLY /K METAKERN.SYS


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.