1.
use "xcopy" to backup something under dos, or use a WinPE bootCD to rescue files you want(especially in NTFS).
2.
use Ghost to dump a current image to another partition, extract when your install completed.
3.
delete the windows directory only, you can re-install a fresh windows to keep some essential files(in most case they are stored in Documents and Seeings)
use "xcopy" to backup something under dos, or use a WinPE bootCD to rescue files you want(especially in NTFS).
2.
use Ghost to dump a current image to another partition, extract when your install completed.
3.
delete the windows directory only, you can re-install a fresh windows to keep some essential files(in most case they are stored in Documents and Seeings)