How do I control other apps with my app?

I am writing an app for a disabled friend. The app displays a form with four buttons. These buttons are meant to act like pressing the arrow keys on the keyboard. The idea being that my friend can use the mouse to click the buttons instead of having to press the arrows on the keybaord.

The problem I have is how do I allow my app to control another app. My app would have to stay active while other apps are running.

I'm using VB5 and I do not know if this is even possible.

Any help would be great. thanks.