If you are using Delphi 3+ and have the ActiveX component VSSpell1, it is very simple to
add a nice spell checker to your TMemo edit applications. (Note: Do not use this
component with a Rich Edit application because of text formatting problems.)
This example is using a main menu click to start the spell checker.
procedure TForm1.SpellCheck1Click(Sender: TObject);
begin
   if Memo1.Text = '' then exit; {If TMemo has no text then don't display spell checker.}
   VSSpell1.CheckText := Memo1.Text;
    If VSSpell1.ResultCode = 0 Then
    Memo1.Text := VSSpell1.Text;
end;

From Clayton Turner