[cloayza]

Yo utilizo esta forma:

Código Delphi [-]
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    Edit1:TEdit;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

Function Execute(Parametros:String):String;

var
  Form1: TForm1;

implementation

{$R *.dfm}

Function Execute(AParametros:String):String;
Begin
      With TForm1.Create(Application) Do
      Begin
             Edit1.Text:=AParametros;
             Result:='';
             If ShowModal=mrOk Then 
                Result:=Edit1.Text

             Free;
      End;
End;
end.

Desde el Form Padre llamo:

Código Delphi [-]
Var    
    sValor:String;
Begin
     sValor:=Unit1.Execute('Parametros');
end;

Saludos...