If I have understood your question correctly what you are trying to do is this
You have two Delphi applications
You want to run App A from App B
You want to debug App B
From what I can tell you are going about this by running App A in your Delphi IDE, perhaps leaving App B open in another instance of D7 and then you expect that the instance running App A will somehow stop at breakpoints you have set in App B?
Now that isn't logical is it.
What you need to do is this
Go to the instance of Delphi where you have opened App B
From the Run menu select Run Parameters
In the Host Application edit box enter the full path to AppA.exe - you should have this compiled and ready
If AppA takes any parameters make sure you supply them
This typically is the way one debugs a DLL called by an app. Not sure what you are trying to do but this is the general area in which you should be looking. If this does not help write back with a clear description of your problem.