[lmikle]

Код:

if Pos(Edit1.Text,Memo1.Lines.text) > 0 Then
  Begin
    Memo1.SelStart := Pos(Edit1.Text,Memo1.Lines.text);
    Memo1.selLength := 0;
  End
Else
  Begin 
     Memo1.Lines.Add(edit1.Text);
  End;