MS-DOS ended with Windows NT. It used file command.com to interpret all DOS commands. Win 2000, XP, Vista use a DOS Shell which emulates DOS but is not really DOS.
DOS is just the operating system just like Windows XP. DOS SHELL is a program in DOS in which you can browse files and open them, etc. Just generally an easier way to move around the DOS operating...
The Last MS Dos Programs where 6.22 which dates back to the late 90's -- three disk set (Floppy) Just run and install. There is a DOS system still running in the background of MS Vista 7.0 but it is...