From the description of your message, I understand that you are interested in uninstalling Vista and install Windows XP Operating System in your HP Pavilion Notebook.
I apologize for any inconvenience this may cause to you.
HP does not recommend installation of XP Operating System on Vista preinstalled notebooks. HP PCs purchased with Windows Vista cannot be downgraded to Windows XP operating system.
This is because the hardware of DV6500 series notebooks are specially made compatible only with Vista and they do not have a compatible drivers for Windows XP.
However, I would like to add that, HP is also providing the pre-installed Windows XP in some of the HP CompaQ Presario Notebooks.
I would like to add that, HP in collaboration with Microsoft are planning to come up with a new package for providing Windows XP with some of the versions of Vista but this may take some time.