The best way to do it is to use the free "gparted", this a boot cd that will boot your computer and list all your hard drives/partitions on your computer. From there just choose what partition you want to reformat. Just remember that when you reformat, everything on that partition is deleted. You can also use the windows installation cd to reformat, but it is a little more complicated. With "gparted" you see exactly what your hard drive looks like and you can make partitions/resize partitions etc. It's a very powerful program. http://gparted.sourceforge.net/index.php
download the gparted live cd 0.3.6.7 ISO. next just use nero or imgburn to burn to a cd. Note it's an 89 mb download. http://sourceforge.net/project/showfiles.php?group_id=115843&package_id=271779
