The first step in creating a popup menu is to select the popup component 
from the component pallet, and drop it on the listbox. Next edit the menu using the menu editor, and select your menu in the Object Inspector for your listbox (see diagram at the right). Once you have completed your menu, select the Events tab in the Object Inspector and double click on the Mouse Down handler to create a new function. You can use the function ItemAtPos to find out which item was selected when the right button is clicked. Finally add the code for the Mouse Down handler (see MouseDown given below).
void __fastcall TSDIAppForm::ListBox1MouseDown(TObject *Sender,
TMouseButton Button, TShiftState Shift, int X, int Y)
{
if(Button==mbRight) // Check to see if right button pressed
{
tagPOINT t;
t.x = X;
t.y = Y;
ListBox1->ItemIndex=ListBox1->ItemAtPos(t,true);
//Sets the index of item.
// If nothing selected deselects
}
} 