[entwisi]

It doesn't touch anything unless you tell it to install. It runs purely from CD(a bit slow obviously as CD is a slow medium compared with Hard disc).

If you need to rescue any data from the drive before re-installing windows it will allow you to squirt the data off the hard disk to either mem stick or over a network (local or interweb) or if there is more than one cd writer in teh machine (laptops obviously tend to just have 1, desktops don't) to disc.