A better way is splitting the drive into two partitions, C:\ and D:\
C:\ is 15GB and gets all the stuff that can go wonky including the OS, your antivirus or firewall, and all the stuff that should be reinstalled on a reinstall like drivers and such.
D:\ is the rest of the drive and contains your program files, documents, music, ect.
When you go to redo Windows, delete the C:\ partition, create a new one over it, and format. You'll have to deal with some programs no longer working and such, but you keep all of your data and settings without having to back them up.