PostMessage # How to pass Message back to Caller EXE??

Question

Hello,
I am new to .net n working with Framework 3.5

Currently working on Application developed in Borland Delphi.
We have 2 exe's named as DBPro.exe and Data.exe

I am rewriting Data.exe which deal with Data Interaction with SQL Server.

Now the project work like, We have button in DBPro.exe which Opens up Data.exe n while doing this it Passes the Message to it using Post Message. I dont have code for DBPro.exe

After All work wen we close Data.Exe it is suppose to PostBack message to Calling Exe i.e. DBPro.exe which will reinitialize it.

I found line PostMessage(HWND_BROADCAST, dbmesg, 0, 0); in Data.exe, in the Form End section which is suppose to Post Back the Message. Now I want to do the same with my new Data.exe. So far I found I can use some invoke method but have no idea how to use it.

I'll appriciate any pointers on this issue.

Thanks.

Some declarations look like this..

 PostMessage(HWND_BROADCAST, dbmesg, 0, 0);
  strpcopy(mstr, 'WM_DBMESG');
  dbmesg:=RegisterWindowMessage (mstr);

I am not able to found any declaration for HWND_BROADCAST