You can tell which HAL or Computer driver the PC is using by
opening Device Manager and expanding the Computer category.
If it says "ACPI Multiprocessor PC" then Hyperthreading is on.
Also, when HT is working, the CPU Category will have two
CPUs shown.
Almost all compliant MBs have an option in Setup to either enable
or disable Hyperthreading. Check your MB manual, for the BIOS
settings. It's usually found in the Advanced category.
You can also download/install & run Everest Home Edition. It's
an inventory program that can display data about your hardware &
software and system configuration:
http://www.lavalys.com/products/download.php?pid=1&lang=en&pageid=3