[Beasty]

It's...just install the OS on the Hard drive...and when turning on the PC, i think you press F9 and it will show you a screen in where you can chose from which hard drive you want to start...chose the one with the OS desired and it's done.
PS: I don't remember very well, correct me if I'm wrong

Yup.

For future reference, that menu your thinking of is called BIOS (Basic Input Output System)