Hi Andy
Try these from the PIC FAQ. ( I usually just set them as outputs)

http://www.piclist.com/techref/piclist/begin.htm
No. 9 from the list
Don't Float: Tie the switch pin Hi or Lo with a ~10K resistor or use internal
pullups to avoid floating inputs when the switch is open. In general, do something
with unused pins don't just leave them floating
also
http://www.piclist.com/techref/logic/xtrapins.htm

>I am currently working on a gadget with a 12C508.  Three I/O pins (GP0, GP1
and GP4) are set as outputs and are used to provide a 'clock pulse' to some
other circuitry.
>
>When used in the field, any or all of these pins could be used, but probably
only two at a time.
>
>Should anything be done with these pins that aren't used?  They will be 'running'
all the time, whether the signal is used or not.  Perhaps tie them to ground
through a 10K resistor?  Or maybe they're fine left open?
>
>What about unused I/O pins that aren't referenced in the program?  Should anything
be done with them?  I'm basically trying to limit long term damage (re: my post
about the life expentancy of a PIC).
>
>Thanks for any input!

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