It is so easy to do the task on your own. Any Linux distro has strong GRUB utility which controls the total boot procedure of single / dual booting systems. 1st install Windows, then install CentOS by inserting DVD / whatever media u have. I hope next procedure u know better. Just follow on screen instructions, only care about the time of partition, don't accept auto proposal, select for custom partition and make rest of the space extended partition. Next u can do easily. After full installation, go to bootloader and mark windows as first booting system and u will be done !