Installing Windows XP in Windows Vista PC

We have been discussing about this afternoon about my husband's HP dv6626 computer that don't have Operating System. Originally, the laptop had a Windows Vista program but was removed in the laptop. My hubby want to put there now a Windows XP program because he don't like Vista. He heard a lot of people complaining about this program. As he inserted an XP CD to install the program, there is a message that says, "no Operating system is found". He tried it a lot of times but still the same problem. Anybody who is a computer genius out there who want to help..appreciate it in advance..Have a nice weekend to all!