Installing a fresh copy of Windows 7 on a computer is fairly easy, here I show the steps. If you want to upgrade your computer from windows XP or upgrade from a 32 bit to 64 bit you will need to do the fresh install just as this video shows.
It is a must to back up your important documents (Pictures, Music, Video, Docs, ect) before installing a fresh copy or upgrading Windows as data loss is possible.
When I can I will use the feature to format the disk which will completely erase the computer. The main advantage is reclaiming all hard disk space.
Remember that after windows is installed you will have to reinstall any software you use like Microsoft Office. If you do not have the installation disks you will not be able to reinstall some software. Free software like Itunes and OpenOffice.Org can be downloaded for free.