Yes, you can disable Hyperthreading in the BIOS, but why would you? Hyperthreading makes the CPU perform better. Is there a reason you're wanting to do this?
Edit: If you're doing this because you have a single threaded app, don't bother. It won't make it run any faster. If it can max out one physical core then disabling Hyperthreading will not make it run faster. In fact, it will hurt performance because the system will have less options on where to assign background tasks.