Broken iPod

My iPod recently broke, and I'm trying to find a solution to fixing it. I believe it's the hard drive (screen and everything else seem to be fine, folder icon and then became sad face after resetting and restoring it a few times). Basically, I'm coming to you asking a few questions:

1) How difficult is it to replace the HDD
2) Is ebay the best source for a new HDD
3) Will any 1.8" HDD work with it, or do I need another 20 GB Toshiba that a seller on ebay says will work with it (it is a fourth gen, 20 gb iPod; not a photo)
4) Could you please direct me to a nice guide to opening the iPod, and replacing the HDD.

I'm fairly tech handy, and have replaced many computer parts in my life and have built one, but haven't done anything with an iPod before. Thank you for your help!