>For an older program, said to be compatible with Windows 3.1 / 95, now (in Windows XP) we get the message "This program requires at least 3 MB of free virtual memory to run". Compatibility mode (Windows 95) doesn't work.
>
>I think I have seen the same messages in two different programs recently. One of them was an older game, which I am sure worked before.
>
>Any idea what I should do to make the program work?

It sounds like a DOS program that is looking for memory above 640K (Expanded or extended memory). This is not the same as NT style virtual memory.

You might look here for some suggestions..

http://dosgamer.com/xp/