iPod classic hard drive upgrade I was reading online that you can replace an iPod classic hard drive, my question is how do you manage to duplicate the iPod OS onto the new hard drive?

How do you mount the iPod classic hard drive to take a backup? What kind of connectors do you use? Is there any way to mount the iPod hard drive onto a Mac, so that I can use the Disk Utility and make DMG's of the software and EFI?
Yes, you can replace the hard drive in an iPod Classic. There is no need to replicate anything on to the drive as all the OS is stored in firmware separate to the drive. Once there is a blank drive in the iPod the firmware will take over. Instructions are here at iFixIt.

Mounting the Classic to take a backup is another question entirely. Since you can't actually get to the OS to back it up the only thing you need to backup is the music and I assume you have a copy of that already. If you don't then I recommend Senuti to recover a copy of your music and playlists to your Mac.