the 571 15" version does not support a 2nd hdd... but the 771 17" version DOES. There are a handful of laptops that I know do, the HP DV7 comes to mind, the 17" version, the 15" DV6 DOES NOT. with the DV7 you have to get the cabling for it.
I have never seen a 15" laptop that supported a 2nd drive internally, and its rare with 17" one, too
Dell business class laptops, Vostro and Inspirion, ect can support a 2nd driver using an adapter in the CD rom bay.