1. How do you reset the NVRAM?

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hold down Command+option+O+F while booting and when you get a cli prompt (Open Firmware) type the following:reset-nvram (press return)

set-defaults (press return)

reset-all (press return)

After reset-all the Mac will reboot.

2. Where is the reset button on these things? Does it have one? On the back panel it says "Reset=Shift, Fn, Ctrl & Start". Will pressing that reset the PMU/CUDA (whatever that is)?

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According to the documents I have that will reset the PMU (Power Management Unit). Wait a good 5 seconds before pressing the power button again after that though.

3. How do you reset the PRAM again? Ctrl-option-PR is it?

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Command+Option+P+R while booting. Hold it down until you hear one additional chime after the initial one.

4. Oh and what's this internal battery - is that the same as the PRAM battery?

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It is kinda an enhanced PRAM batt that can keep the computer running while sleeping for a while so you do not have to shut down to swap main batts.
Information about the Wallstreet and PDQ internal backup battery can be found here:

http://www.macshadows.com/forums/index.php?s=&showtopic=7347&view=findpost&p=54594