after a little over a week of getting aquaitned with my new, beloved PowerBook 17", I am setting up Firevault so my parents can do taxes on it. I figured while i was at it, i might as well set it up on all four accounts on this computer. however, after setting it up on my acount (comp. admin), the button was in a gray-state (frozen-like) where it says "Turn On Firevault..." it looks the same on my dad's, moms, and guest account. is there any way, or is it just for ONE account? also, does firevault in any way slow down the performance of the machine?