For Windows, it may be difficult without a CDROM, but for MS-DOS it's quite easy. You can create a "Windows startup disk" in any Windows 9x/ME using "Control Panel" > "Add/Remove". You may also find floppy images on the net.
- Boot with your floppy
- Choose the second option (something like boot without CD support)
- IIRC, MS-DOS needs to boot from the first primary BIOS partition, so "fdisk", remove the first - non-DOS - partition (probably your FreeBSD slice) and create a primary partition for DOS.
- Exit fdisk and reboot
- From the floppy do a "format /s c:" This will format the partition in FAT and copy the appropriate system files
- Remove the floppy and reboot. You'll hopefully boot from c:
Now you can reinstall FreeBSD. Fun, eh?
You may also use dosbox or wine (as suggested by ale). MS-DOS is super fast on Qemu (suggested by rocky) but Windows is so unbearable you'll hardly be able to finish the setup, let alone run it productively.
