Hyperthreading is turned on in the BIOS. On my MSI mobo, the option is under advanced chip options (or something like that).
If you're running windows, you may have to reinstall for it to act like it has two processors. I installed Win2000 on my computer, without turning on HT. Later decided to try it out, but win2000 didn't want to act like it had two processors. Left it on, and forgot about it, eventually had to reinstall windows. Win2000 saw two processors after reinstall.