This is a DUH! question. Trying to boot off an external firewire drive attached to a 24" iMac. I go to SYS PREF and select the Firewire drive to start off and restart but it continues to boot off internal drive. What is the key I press at power up to allow me to select the drive from the keyboard????? I should know this, but I forgot. I am using a WIRELESS keyboard, is that an issue??? Thanks!!!