MultiArcade posted a howto on upgrading the iPod nano from 4GB to 8GB.
Here are the first three steps:
1. Buy a broken 4 gig Nano from Ebay (black or white).
2. Buy a working 4 gig Nano anywhere (black or white).
3. Open up both Nanos. I used a razor blade to pop open the plastic Nano case. You do not have to remove the switch just pry a razor blade between the steel case and plastic case and they will pop apart after prying up and down the nano (about 5 minutes).