Resizing a partition in a hard disk is a way to better manage a hard drive's resources. Several tools may be used for resizing.
QtParted available in Knoppix distro.
Is probably most popular commercial tool for resizing partitions.
Is a free DOS resizer utility. It's best advised to be used from within a floppy boot disk or USB boot drive. It does not resize an NTFS(WinXP,2k) partition.