An easy way is just to use the FindWindow() Win32 call. You can use Spy++ to find out the class name of the window and get a handle to it. Now you can use the handle to send it messages. There is a harder way using Hooks but it requires writing a DLL and some other nastiness.

There are tons of ways to talk between processes, and depending on what you need to do, you can choose the best way. Search for IPC on MSDN.

If your app wants to launch a web page, you probably want to use ShellExecute(handle, "open", "http://www.gamedev.net", NULL, NULL, SW_SHOWNORMAL);. It''s not much of communicating between process, it''s a windows mechanism to start the pre-defined program.

- Windows messages is another way as AP mentioned. Typically old programs use this. It''s quite simple to use if you have two GUI applications. The sender does FindWindow followed by SendMessage/PostMessage. The receiver simply picks upp messages in it''s message loop. There are drawbacks with messages, for instance it''s harder to tighten security.

Sockets is one way, even if the two programs are on the same machine.

Pipes is another way, which probably performs best if you need to pass a lot of data.

Shared memory between two (or more) applications.

MSMQ can be used between processes, even on different machines. It''s good for reliability if you need to queue up messages and make sure they don''t get lost. It''s however way overkill if you need some simple IPC between two simple programs.

I would assume a popup killer to benefit from Internet Explorer plugins (ie. not be a standalone program). Not sure, but you could probably handle the DWebBrowserEvents2::OnBeforeNavigate event to prevent a popup window from getting created if certain conditions are fulfilled.

If you''re not passing data, but simply signalling between two applications, there are OS objects such as Mutexes.

There are even more ways to do IPC. Read more here: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ipc/base/interprocess_communications.asp