I guess you are on the usual case where you want to have Linux and Windows running at the same time.
Setting up a dual boot is fairly simple. The easyest way is to : 1) Download the linux distribution you want to have, and burn it on a CD-ROM 2) Install windows, or keep your already installed version 3) Install your linux distribution. 3.a) Insert your CD in your CD-ROM drive 3.b) Reboot (if it doesn't start the installer automaticly, search on any search engeine how to do that, it's easy) 3.c) During the installation process, there usually is a question asking you how much space on your hard disk you want to dedicate to linux. Give the amount of space you want. 3.d) The linux installer should detect the presence of windows, and automatically make it available at the boot menu (a menu that allows you to choose between severall operating systems).