How can one break a large file like a movie into small pieces using DOS and then re-group it back into a single original file?
Do you really want something that will work in a version of DOS or something that works on the Windows command line? Command line versions of the above mentioned archivers can do the trick as will HJ-Split, the DOS version of which is located here: http://www.freebyte.com/download/hjsplit/hjspldos.zip.
Archiving software can do this for you. There is no command to my knowledge, in Windows, that will let you split files.
Winrar, Winzip or 7zip should do the trick.