Communication between two exe. i.e. When second starts disable screen of first

I have a .exe called menu.exe On that screen are 2 listboxes.

When i chose from the menu to run another program, say herman.exe, the menu.exe will keep running. The second exe. herman.exe, will get focus. But the two lisboxes, or the frmmenu, from menu.exe should be set to Enabled = false,

When stopping the herman.exe then menu.exe must get the focus and the two listboxes, or the frmmenu, should be set to Enabled = True.

Herman