???Sending a structure with windows messaging???

 How can you send a structure to a component in another application
using windows messaging?  I plan on sending the handle of the component
to the app that will communicate with it and I just need to send the
message to the components handle with the structure.

I want to send something like the following:

TMessageStruct = record
    Param1:  String;
    Param2:  Single;
    Param3: Word;
    Param4: Integer;

SendMessage or PostMessage won't work...

I see in the VCL they intercept all sorts of structures like the one
above, but
I don't understand how the messages are actually being sent to the
component(like a button), for example how does a button down message
actually get sent to the button component???

ANY help would be appreciated!