Mark Bailey had documented a way to dual-boot FreeDOS with Windows XP, without having to re-install Windows.
You can install FreeDOS on a new computer and have it dual-boot with Windows XP as well. This doesn't harm the WindowsXP installation at all and doesn't require re-installing WindowsXP. You just put FreeDOS on a trivial amount of disk space at the end of the drive.
I worked out a detailed procedure for doing this and would welcome comments. It uses free tools that the Linux guys use for dual booting.
See www.k1ea.com/hints Dual-boot "Real" DOS on Windows XP for a detailed procedure, though a bit MS-DOS centric. The keys are shrinking the NTFS partition to make room for DOS, formatting a FAT32 partition, and configuring the dual boot.