NTVDM.exe
(Microsoft)
Windows NT Virtual DOS Machine Windows NT4/2000/XP. Whenever you start a DOS program under Windows NT4/2000/XP, that DOS program gets run by the Windows NT Virtual DOS Machine, NTVDM, which basically emulates a DOS environment so that your program can run. There will be a different instance of NTVDM running for each DOS program that you run.
Recommendation :
If NTVDM is in your Task List, you have a DOS program running. If it is twice in your Task List, you have two DOS programs running, etc... Leave alone; as soon as you close your running DOS program(s), NTVDM will disappear from your Task List.