Windows 8 - Windows 7 Dual Boot?

My laptop has recently broke down and not worth fixing as the motherboard has finally gone so I am just keeping it for spare parts RAM > HDD etc. Now I purchased a new laptop and it has Windows 8 :(

The problem is with windows 8 installed on it and my girlfriend likes it and would like to keep it. So I was just going to partition the hard drive and install windows 7 on the partition (easy enough you would think) until I read this

Warning

You must install the older operating system first, and then install the more recent operating system. If you don't (for example, if you install Windows Vista on a computer already running Windows 7), you can render your system inoperable. This can happen because earlier versions of Windows don't recognize the startup files used in more recent versions of Windows and can overwrite them.

I will admit I am being lazy and I should just format the drive and install windows 7 as a fresh install and then install windows 8 on a partition so I can dual boot the operating systems but what I don't get is how this effects the start up files as at all as if we partition the HDD as all windows 8 start up files should already be installed on the first half of the partition, so lets say I create a separate partition on the drive and install windows 7 all the start up files should install on that half of the operating system.

For some reason I am thinking you may not get the option to choose which operating system you wish to boot at worst case scenario.

As I always would of thought the BIOS would recognise the HDD has 2 partitions and you could load either operating system providing you choose to either by accessing the bios and setting boot priority or simply choosing what you want part of the HDD you want to load first before windows even starts to boot anything 7 or 8.