Upgrade Hard Drive?

My battery is pretty much dead so I'm most likely going to crack her open soon. In the past I tried to drop a 40 GB hard drive in there, but I couldn't get the iPod to recognize it. I might be willing to try it again. Anyone have any success with this?

Also, I might not. There is a line in the display and every once in a while it just freaks out and instead of playing songs, it just skips to the next one. So it might be time for an upgrade. But I think this is the coolest looking iPod case design so I'd prefer to keep it.

Any thoughts?

Thanks for the answers everyone. What happened last time was that I put a 40GB in it and when I tried to boot it to anything the drive just kept ticking like it was resetting.

If money drops from the sky and I can afford the HD and battery I'll try it again. And Kyle, I will buy from iFixit!