What they are asking you to do is remove the hard drive from the external casing and place in inside of the computer. This may give you a better chance at file recovery. Some of the dos based recovery tools may or may not detect the USB drive... but having it a slave would give you your best chances. Try these sites for how to:
http://tech.yahoo.com/gd/adding-a-se...o-your-pc/2988
http://www.basichardware.com/HowTo_I...ard_Drive.html
Make sure that when you open the external housing up that you take a look at what brand the drive is, this will help you select the correct diagnostic tools.