First, make sure your Windows license isn't OEM version - as you will have to purchase a new copy of Windows (it is paired with the mobo/CPU).
Second, backup your data to another hard drive - this is very important, as even a reinstall over the top can lose your data.
Third, install the OS, wiping the partitions and creating new ones. You will be asked for your product key - enter it so your Windows will be activated. Then install all of the patches/updates.
Last, restore your data.
I am looking to do a fresh install of Windows 7 so I don't want to keep everything on my computer, I want to start over. So what do I have to do prior to putting in the new mobo and cpu and after putting in the new mobo and cpu?