sleep computer on keyboard idle time NOT mouse idle time

[mahaju]

The is probably not very clear but this is what I want
I want to make the computer go to sleep (or shutdown) if it is idle for ,say, 30 minutes, like windows power option
How do I do this?
I also have another requirement.
Can I make Puppy's the idle time counter ignore mouse movement?
That is, if the keyboard is idle for 30 minutes then the computer can go to sleep, but I should be able to move the mouse during this time, and it should not reset the computer's idle time counter
So the computer should go to sleep even if I do move the mouse, as long as I don't press the keyboard (for a specified amount of time)
Is it possible to do this?
Thank you