How do I Stop a key from booting my system.

I'm trying to figure out how to stop the esc key from power on my computer.
It doesn't do it if I've turned off the PSU recently, and the BIOS settings
are all set to disable for USB/Keyboard/Mouse/etc powering on the system...
but if I've booted to Vista once, then shut-down the esc key will now power
on the computer. As there are many cats running around my house, so far
almost every time I've left the house, I've returned to my computer on :P
I've been poking around the Power Settings and other such options but I can't
seem to find any option to stop Vista from turning my computer on. It's not
the sleep option either that I'm choosing, It's "shut down" on the shut down
button. Any ideas/answers? Thanks in advance.

-Peace