This question has been asked and answered scores of times on these forums alone, in just the last month or two. Did you even TRY searching with Google before posting?
And don't forget to make sure there are XP drivers for the rest of your laptop's hardware. Not all new systems have them, and if yours is one of them, you're SOL. Sell the system on ebay and use the money to buy a laptop with XP, or learn to live with Vista. On an HP laptop, I'm sure that will be painful, but XP won't likely be much better if the underlying hardware is the usual HP crap quality.
I have a HUGE problem. When I formatted my New Hp Laptop thats running on vista it indicates that there is no hard drive when I tried to install Windows XP. I cant seem to find the problem. I looked in the Bios setting and it says that my first boot is in fact the HD, I dont know what it wrong. Im getting Frustrated!!!