Problem with my windows xp

Hi,
I recently upgraded my HP laptop with windows xp and windows 2003 server dual booting. I now see a message on my comp which says that my windows xp os is not genuine os. The hardware guy had not installed a genuine os for me. I can ask him to rectify the problem but just thought if I could fix it myself. I have with me the windows xp dvd which came along with my laptop which I used twice already when I had a single os. Now with the dual os on my laptop how can I reinstall windows xp alone. Please help.