Finding out what type of hard drive is installed inside your system is pretty easy. Just pop off the side of the case, look where the hard drive connects to the motherboard cable, if the cables end connector is primarily black in color and smaller than a standard IDE ribbon connector, than safe bet you got yourself a SATA drive. But if the drive is connected via what appears to be a very "ribbon" looking cable and the end connectors are "gray" in color than you got an IDE drive.
And in regards to installing a Windows XP Operating System from an "on-line" source, I would have to balk on that idea. I've never installed an O.S. from the Internet, I have done across network installs of O.S.'s over an in house network, but you can't do that sort of thing from an "on-line" source. Are you sure that you don't have a Windows XP install disk? I only ask for the most part, computers back in the days of Windows XP that shipped new, normally came with a couple of support disks, a proprietary, in your case, Hewlett Packard program recovery disk and a Windows XP re-install or repair disk.
If you truly don't have any type or types of disks at all, do not under any condition go to any of the various P2P or Torrent sites and download a "boot legged" copy of an Operating System and install it, not very safe, nor very legal. You might have to make a drive to your local computer store and look in their software section and scout out if they have a Windows XP Operating System. If they got one, preferably one that is up to (Service Pack 3) out of the box, go ahead and grab it, it will work and you can then rest assured that if an install is ever needed in the future, your covered.
Keep us all in the loop here, check in and let us know what's going on as so we know where your at in the process and can advise when possible.