Problems Running Some Old Programs

Hey, I want to run some old (or at least i think they're old) programs. A lot of program (even the latest versions found via the internet) give this box when trying to open:

C:\PROGRAM FILES\BLABLABLABLABLA\PROGRAM.EXE
C:\WINDOWS\SYSTEM32\AUTOEXEC.NT. The system file is not suitable for running MS-DOS and Microsoft Windows applications. Choose 'Close' to terminate the application.

It gives me two buttons: Close and Ignore. When I click either of them, the program just closes. How do I get rid of this box? Thanks alot for your time.

 

Ahh yes, i forgot to mention that i have also this really old computer. I recently installed Windows XP on it and even though it runs very slowly, these programs DO work. Please help!!