Creating New Keyboard Shortcuts

I am new to the Mac world but glad to be here. I have a new iMac with the wired apple keyboard with numeric pad. I have been trying to setup the F16 key to start my email program. I went to System Preferences, keyboard, shortcuts, applications and found Entrourage. I mapped F16 to it, but nothing happens when i hit F16. Even stranger, when i reopen System Preferences it shows that the shortcut to entourage, which did show F16 when i left it, now shows just 6. Help please.