must P09
If you have Service Pack 1 installed, then if HT is enabled either
deliberately or accidentally in the BIOS, the OS will automatically detect
it and use it - you'll see it detect an "ACPI Multiprocessor PC" device at
boot, then be prompted for a reboot.
If you do not have SP1, then XP will ignore the presence of HT until you
install SP1 or re-install the OS - however, no harm will be done.