procedure TForm1.Button1Click(Sender: TObject);
var
SearchRec:TSearchRec;
ext,AppPath:string;
begin
listbox1.Items.Clear;
AppPath:='d:\test\';
ext:='*.txt';
FindFirst(AppPath+ext,faAnyFile-faDirectory,SearchRec);
listbox1.Items.Add(SearchRec.Name);
while FindNext(SearchRec)=0 do
listbox1.Items.Add(SearchRec.Name);
end;