iFixit

There are five retaining tabs on each side of the iPod.

With the large iPod opening tool still inserted in the top seam, press a small iPod opening tool into the gap you just created.

Run the iPod opening tool down the side seam, releasing all five tabs.

It may be necessary to wiggle the tool while working your way down the seam to free all the tabs.

Run the iPod opening tool around the lower left corner of the iPod and along the bottom seam to free the two retaining tabs near the dock connector.

Run the tool around the lower right corner of the iPod and along the right side seam to free all five retaining tabs.

The case of the iPod should now easily come loose. Ensure all retaining tabs are free before proceeding.