Point 1: A USB 2.0 external hard drive is nothing but 2 different components
a. A hard drive, just like the hard drive on which your copy of XP is installed.
b. A shell which contains that hard drive. The shell connectors for the drive and (should have) an external power supply of its own.
Point 2: Manufacturers of hard drives make both PATA and SATA models of the same drive. The way to differentiate is to look at the serial number on the drive.
Point 3: Any drive which is in an external shell...can be removed from that shell and directly connected to a motherboard with the proper connectors on it. SATA connectors are clearly different from PATA/IDE connections on a motherboard.http://www.directron.com/patasata.html
As you can see, IDE motherboard connectors are much larger.