Alt+tab switch not working between DOS and windows screens

I have a problem again. I hope someone can help me.
On my IBM machine I have installed windows 7, clean install. I have to use a very old DOS program. It works without a problem. On clicking its bat file, it opens a full screen command .com window it runs smoothly. The problem is, i can not switch between this and windows 7 with alt+tab. Every time i try i get a black screen. And I have to shut down the windows.
With XP, we could arrange the PIF file, or BAT file, give the instructions so that alt+tab, alt+windows would work. But I could not find a way to do it with windows 7. Any help will be appreciated.
Thanks in advance