Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

function GetTempFile(const Extension: string): string;
 var
   Buffer: array[0..MAX_PATH] of Char;
   aFile: string;
 begin
   repeat
     GetTempPath(SizeOf(Buffer) - 1, Buffer);
     GetTempFileName(Buffer, '~', 0, Buffer);
     Result := ChangeFileExt(Buffer, Extension);
   until not FileExists(Result);
 end;

 procedure TForm1.Button1Click(Sender: TObject);
 begin
   ShowMessage(GetTempFile('.~tp'));
   // The temp. file looks like C:\WINDOWS\TEMP\~61D5.TMP 
end;

  { 
  Note: 
  The GetTempFile function just returns a unique filename but 
  doesn't create the file. 
}

 { 
  Bemerkung: 
  Die GetTempFile Funktion liefert nur den Namen der temp. 
  Datei aber erstellt sie nicht. 
}