This one doesn't pertain to me so much but for my wife and the other 60 billion people with iPods, here is a way to quickly recall the various modes. For instance, the image here shows how to get into Diagnostic mode with a "fifth generation click wheel".
If your wheel looks different, click the image shown and you will go to the Command-tab site. They have several versions on display as well as shortcuts on getting into Disk Mode and doing a hard reset.
PS - yes, 60 billion is a slight exaggeration.
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