Having had difficulties opening my own iPod classic (generation 6), I thought I'd try to make it easier to others:
My aim here is to illustrate the design of the clips that hold the casing together, so that you wont be working blindly at this.
(click on images to enlarge)
In the cross section above the clips are drawn in red: They are point welded to the inside of the back cover (blue line). The clips lock into grooves in flanges on the front cover (black line).
Then, while creating the opening, use another tool to unlock the clips. To keep the opening some stick in guitar picks.
Work your way round the iPod. Pay attention to ribbon-cables when unlocked and please look for further instructions via link at end of post.
This is where the clips are (red circles).
Orange arrow points to pocket-like parts of the structure, that does not have to do with the clips. You will see them when you make the opening, and you can use them to locate the clips.
And this is where the clips go (view of side...upside down, sorry)
Same (view of top)
Same (view of bottom)
Getting it opened is in my view the hard part. Have fun inside.
Lots of guides and trubleshooting here for what ever you want to fix: http://www.ifixit.com/Device/iPod_Classic
I hope this is helpfull.
iPod, iPod classic, repair, how to open, lock, clips, illustration, drawing, image, picture