You do NOT "configure and customize window 7 to window 8".. Windows 8 would have to be installed either as an Upgrade, or as a clean Install.
If you are asking how to run BOTH windows 7 and Windows 8 on the same computer, Thats refered to as daul boot.
Daul boot is best done using TWO HDDs. If Windows 7 is already installed on one HDD:
.. simply disconnect it and connect a 2nd HDD and install windows 8.
.. Once win 8 is installed you can re-connect first HDD (w/Windows 7).
.. You then set boot priority to the OS drive you think you will use most often - NO sweat can change.
OK You want to boot to the other OS - when you power on during the POST you simply hit the "Hot" key that will display a boot menu. My Gigabyte MB it is F12 and on my Asrock MB it is F11. Reboot and unless you hit the Hot key again you will boot into the OS you selected in BIOS boot priority.
YOU BUY Windows 8 upgrade.
There is NO way around having to buy Windows 8, either OEM of Upgrade version.
In many cases the Cost does NOT justify the performance gains.
When you couyld get windows 8 upgrade for 15->60 bucks it was not a bad option. 60+ it becomes very questionable as to cost effectiveness.