You need to install SATA drivers [u]as part of the XP install.[/u]
The installer will prompt you for SATA drivers, you respond by pressing 'F6' at the appropriate moment, the installer will then ask for the drivers, you then insert the floppy into the USB floppy drive.
Then the XP installer carries on as usual.
If you didn't install the SATA drivers, the installer would timeout with the request, then carry on to the end of the installation routine. However, when you removed the XP installer disc and rebooted - the boot would FAIL because XP wouldn't be able to read from its own SATA HDD.
There are many users that have fallen foul of this, thinking the installation was OK because it ran to the end and 'completed'.
XP cannot load SATA drivers from any media except a 3.5in floppy. (Although I have heard of instances where it CAN be done with a CD).
You'll need to go to the HP website and download the SATA drivers for your system.