Multi Threading and forms

Hi Experts,

     I have a form with a text box and a command button.  When the user presses the command button, I want to create two seperate instances of the same class and have them run on a thread of there own.  The threads will each come up with a random number between 1 and 10.  When the threads are done I want the form to take the two randomly generated numbers, add them up, and display the added value in the text box.

Something like this:

Form1.cs:
namespace MyNameSpace
{
           Public Partial Class MyForm : Form
           {
                      MyClass class1 = new MyClass;
                      MyClass class2 = new MyClass;
                     
                      class1.StartThread();
                      class2.StartThread();
           

                      Public void AddThem()
                      {
                                  txtBox.Text=class1.Result+class2.Result;
                      }

           }
}

MyClass.cs:
namespace MyNameSpace
{
           public class MyClass
           {
                      int RandNum;
                     
                      public int Result
                      {
                                 get
                                 {
                                              return RandNum;
                                  }
                                  set
                                  {
                                   }
                       }

                      public void StartThread()
                      {
                                 Thread t = new Thread(new ThreadStart(ThreadJob));
                                 t.IsBackground = true;
                                 t.Start();
                       }

                       private void ThreadJob()
                      {
                                 RandNum=GetRandomNum();
                                 myForm.AddThem();
                       }
}

What I am basically having problems with is how to call a function that only exists in the form's code from the class threads.  I know that in my example I could have a zero value for Class1.Result or Class2.Result depending on which thread finished first, but I am not worried about that for now.  I need the classes to be on their own threads so that the GUI is still functioning while my classes are coming up with the random numbers.  I know that in this example I wouldn't need to use mutliple threads, but this is just an example.  In reality ThreadJob takes about 30 seconds to execute.

Any help would be appreciated,

Thanks,
axnst2