If you have a computer where you already installed Windows and you wish to install Linux as well (dual boot), you may want to resize the NTFS partition to get more space for the Linux partitions.
One way it to use Gparted (Gnome Partition Editor) – http://gparted.sourceforge.net/
with a boot CD. Here are the instructions:
• Boot from the CD
• Hit <ENTER> when you see the message “Boot:”.
• Select language, keyboard and screen resolution from the menus.
• The partitioner should start and the following steps are intuitive
More details are available @
It is also possible to do it with a USB Thumdrive if you do not want to burn a CD and your bios can support booting from a USB device.