You need to boot your computer from a DVD, CD or floppy disk that has been prepared to be bootable and contains the Ghost 2003 DOS program.
If you originally got your Ghost 2003 on a CD, it might be bootable - you can try it and see.
Depending on how you made your DVD containing the Ghost files, it may or may not be bootable.
Otherwise you need to make a new bootable disc or floppy from within Ghost 2003.
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