[No, you could run a type of dos in Windows 95,2000, XP and I see no way to run it in my borrowed Vista computer.]
Goto the windows search box, type in "command" and press enter. That will take you to a command (DOS) prompt - but that's not really DOS. Depending upon how your real time program interacts with hardware, it may or may not run... but if it ran under the XP command prompt, I'd expect it probably would run under Vista or Win 7.... probably.
[I need a floppy drive for an old real time program that will work only under dos.]
Is the disk 5.25 or 3.5 inch?
[I asked about windows 7 because all info on vista says it will not see a usb to floppy drive. ]
Google search returns numerous hits for floppy drives claiming Vista compatibility - but, I'd suspect, only 3.5"
If your app is on a 5.25" inch disk and you have no 5.25 drive available, there are services that can transfer the software to another medium for you.
Alternatively, if your PC has an open 5.25" bay, you should be able to install a 5.25 floppy drive - presuming your bios will recognize and allow you to configure for it.
Once you get the software transfered, the next step would be to run the app either from the commnd prompt or from within one of the virtual Dos simulators that others have suggested on the thread.
Good Luck,
=Bill