I cannot express the amount of years and time I’ve wanted to know this exact knowledge but never quite gained it despite creating multiple boot environments and even using these “simple” third party tools. Now I get IT!
Unfortunately I didn’t find this information 10 months ago so I’m currently dual booting Vista & XP the “bad” Microsoft way. This unfortunately means I no longer have the pre-boot XP menu choices but instead these only are offered for Vista. So I hope I never have a need to boot to “last known good” in XP on that machine.