They need to be pointy like a small flat-head screwdriver, except it has to be made of hard plastic so that you don't dent the metal case and gouge the plastic case. But it has to be hard enough so that you can pry open the seam between the two halves of the case. Someone once posted that a guitar pick works, but I don't know the technique for using it to open the case.
Here's how with the two tools. They look like this, BTW.
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Use the wider one (if they are different) to pry open the seam at the top middle of the iPod, just enough to insert the tool's tip into the metal half of the case. Push against the plastic half to create the initial gap. You want to start at the top because there are no clips along that edge.
Looking at the iPod from the front, insert the second tool to the right of the first one. While putting pressure on the tool to push it into the metal half, move it along the seam to the right around the top right corner and down the right side. If you are pushing down while you do this, it should pop open on the right side by the time you get about halfway down to the bottom right corner.
Then, open it like a book from the right side. Be careful not to yank it open on the left side, because there is a delicate ribbon cable at the top left corner that connects the two halves of the case. Carefully disconnect the ribbon cables socket to separate the two sides of the case.
Tip when reassembling: Make sure the external
hold switch aligns with the internal switch on the logic board. You'll see what I mean. If you forget, the hold switch won't work, and you'll have to open the case again.
You can find an online guide with pictures at
http://www.ifixit.com/
(I'd give you the exact link, but the site was down for maintenance.)
Note: The technique is the same for a 4th gen iPod, except you don't need to worry about aligning the hold switch. I've never opened a 5th gen or later iPod.