From Windows XP help and support.
To create an MS-DOS startup disk
The MS-DOS startup disk you create will allow you to boot into MS-DOS.
1. Insert a floppy disk into your computer's floppy drive.
2. Open My Computer, and then click the floppy disk drive to select it.
3. On the File menu, point to the name of the floppy drive, and then click Format.
4. Under Format options, click Create an MS-DOS startup disk.
5. Click Start.