Pass value between forms

[Memnoch1207]

I have 2 forms (Main and Username).
My Main form has a mainMenu and a dropdown list (combobox) which displays usernames. The mainMenu allows an person to click the "Add User" menu item, which then displays my Username form, which is basically a simple input box, when the user clicks the Submit button on the Username form I want the username to be added to the cboUsers drop down box on the Main form...something like this.

In Username form

private void button1_Click(object sender, System.EventArgs e)
{
   //Add the username to the Main forms Username dropdown list
   
   Main.cboUsername.Items.Add(txtUsername.Text);	
}

but obviously, it doesn't work that way...any ideas on how to get this to work?