I assume the iPod was set to mass storage mode before you tried this, but if it wasn’t…
Anyway, barring that, I’m pretty sure I know whats wrong, but first I want to clear this up: you switched HDs, the laptop works, but the you can’t see the old HD’s data through the iPod.
So if my understanding is correct, the problem is both of the partitions on the laptop’s old HD are NTFS formatted. (thats how they ship from Sony and its better for most things) The iPod, even in mass storage mode, cannot read NTFS; Mac OS itself has problems too; only Windows and Linux can access a NTFS partition. So I don’t think you can access the old HD’s files through you’re iPod. (no idea really, iPod linux might do the trick)
But there is hope ; you can buy an external 1.8in usb enclosure and that should let you access the hard drive. They can be had for less than 20usd.