drawing on another window

[dave2k]

i would like to draw a see through rectangle with red border at a certain position on another programswindow. I was wondering how i would start going abouit this?q

[Mike Harnad]

Working backwards...

In order to draw on a window, you need an HDC.
To get the HDC, you need a window handle (HWND).
To get the HWND of another program, take a look at FindWindow(), or, EnumWindows().