Please fill out the system specs.
Is this a new computer that came with Windows 7?
If so you will need to go to HP's web site and look it up to see if they have the drivers for Windows XP. Many of the laptop/notebook/netbooks vendors no longer have drivers for machines loaded with Windows 7. I have run into this several times, where special software would not work in Windows 7 so they needed to downgrade, then we found out we could not load XP on the machine because there were no drivers. If HP has the drivers you will need to download them and copy them to floppy disks, especially the drivers for the Hard Drive controller, Video Card, and Network Card. Once you have those 3 running you can download the rest from the internet, etc. However I would have them ready on a USB drive much better than downloading while setting up the machine fresh. Make sure you apply service pack 3 as soon as possible so you will have base firewall protection before you go surfing the internet.
Good Luck.