How to install 2 window in your computer

If you like to use window 7, but your window vista is genuine.
you want to keep your vista but wanna use window 7 as well.
you can have 2 windows at the same time!
not really complicated, just divide 2 partition of your harddisk.
then C drive running window vista, D drive running window 7.
when you startup your computer,
it will ask you to choose whether you wanna use which window.

For Window XP, it will shows 'Earlier version of Window'
For Window Vista/7, it will just shows 'Window vista/window seven'