I code in Delphi rather than in Visual Basic, and so, AFAIK it is possible to change opacity of another window with use of function
SetLayeredWindowAttributes. Just google about it.
What is more, one shoud change an attribute of the specified window (namely add 0x00080000 to an extended window style) to allow opacity effects.
But why not completely hide that window by means of Win32 API? The effect will be the same...
I am still learning English