Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

procedure SetAsMainForm(aForm:TForm);
 var
   P:Pointer;
 begin
   P := @Application.Mainform;
   Pointer(P^) := aForm;
 end;

 {************************************}

 // Example of Usage: 

{ 
Question: 

  If my application is main.exe and the main form is form1, form1 displays 
  when it runs. I would like to display other forms based on the parameter 
  passed. 
  main.exe param1 will display form2 as the first form 
  main.exe param2 with display form3 as the first form 

Answer: 
}

 program Project1;

 uses
   Forms,
   Unit1 in 'Unit1.pas' {Form1},
   Unit2 in 'Unit2.pas' {Form2},
   Unit3 in 'Unit3.pas' {Form3};

 {$R *.res}

 procedure SetAsMainForm(aForm:TForm);
 var
   P:Pointer;
 begin
   P := @Application.Mainform;
   Pointer(P^) := aForm;
 end;

 begin
   Application.Initialize;
   Application.CreateForm(TForm1, Form1);
   Application.CreateForm(TForm2, Form2);
   Application.CreateForm(TForm3, Form3);

   if Paramstr(1) = 'Param1' then
     SetAsMainForm(Form2);

   if Paramstr(1) = 'Param2' then
     SetAsMainForm(Form3);

   Application.Run;
 end.