Shutting down vs Power Off in virtualbox

[rye9]

When I want to finish a session of using Vista in VirtualBox.... if I "x" out the application, "it says "save in state" or something like that and "power off machine"... is power off machine different than shutting down windows? What's best to do and what does what?

I'm assuming also that I can't just close virtualbox and come back to it later without windows being shut down or affected?

[rye9]

Bump? Plus... How do I adjust the window size for Virtualbox/vista? I have it set to 1024 x 768... However it's a little too tall. Plus, I istalled the original COD and idk if it will fill the screen like it should... I fear it will
just fill the small window virtualbox gives it