[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)

well, that's the Main Menu, the menu i'm talking about is the Boot Up Menu

you can choose between OS's if you have more than one partioned on a hard drive with romboot or biosloader.