its a security feature from apple, you cannot transfer your itunes from one pc to another, and as far as im aware changing your hard drive will confuse itunes enough to tell it that your trying to rip the itunes from your ipod to another pc
download a program called ipodrip and run it, it will allow you to rip all the tracks off the ipod into mp3 format on the pc, then just drag the mp3's into your itunes, and bobs your uncle, itunes restored.
hope that helps
"You only live once, play it right, and once is enough" - me :)
"When i die only god can take my soul" - me again! :P