I think the reason for this is that SetWindowsText does not change textbox text.

I should''ve read the docs more carefuly: "SetWindowText cannot change the text of a control in another application." Try WM_SETTEXT instead. Make sure you SendMessage it.

The reason is that each process has its own address space. When you pass the window text to a function, you give it a pointer. In another process, this pointer points to (most likely) some unaccessible data. What are the chances of AIM''s process having the string "My new title" in its address space at the exact same memory location as it''s in your app''s address space?

This is why you can''t subclass windows from other process (that is, you can''s SetWindowLong(GWL_WNDPROC) if the window does not belong to your process). Windows does allow certain messages to cross process boundaries, for comparibility with Win16 code. I believe WM_SETTEXT is one of them. The "proper" way to send data to another process is with WM_COPYDATA.

There is a way do whatever you want with any process. To do this, you need to inject a dll into the address space of another process, and let the dll do the work. One way is to use hooks. A more interesting way would be to allocate memory in another process, copy your code into it, and execute it.

If you wonder where I got all of this, it''s from Jeffrey Richter''s "Advanced Windows" book. He also has sample programs that do what I''ve described here.

Ok, so lets say I do a SendMessage:
SendMessage(h, WM_SETTEXT, ?, ?);
What would the wparam and lparam be?

Ok, well I guess this is a little far-fetched for me I guess. I''ll have to wait till I learn more about windows programming.