¿Cómo hacer un disco de Arranque MS-DOS con un pendrive?

Ésto también funciona con cds, no sólo para pendrives.

1 Download  Windows 98 System Files 
2 extract 

3  Make a bootable USB Key to boot into a DOS environment.
Your computer must support booting from a USB device in order to boot from the USB Memory Key.

• Download  HP USB Disk Format Tool
• Insert the USB Memory Key into the USB port of your computer
• Launch the HP USB Disk Format Tool program
• Under the device drop down list, make sure that the USB memory key is selected
• Under the file system drop down list, select FAT32
• Enter a Volume label if you want one
• Check the box next to Create a DOS startup disk
• Select using DOS system files located at:
• Then click on the square box with 3 dots on it on the right hand side
• Browse to the folder where you extracted the Win98 System Files and click OK 
• Now click the Start button
• Click the Yes button in the warning message

Your USB memory key is now being formated (may take a while) and the DOS system files will be copied onto it.
Once the program has completed the operation, click on the close button. You now have a bootable USB memory key.

fuente: http://naja-also.blogspot.com.ar/2012/06/western-digital-idle-head-parking-issue.html?showComment=1347169767229#c6537714484671714282