Intel earlier versions of the hyperthreading processor yes can
disable one virtual core.
As for the core duo if its has build in speedstep technology, there
will be power management so don't worry about processor drawing
more power and draining batteries.
Its 2 physical core and maybe you can rea your motherboard or
processor user guide or do a search over the internet to see if
there is any way to disabble one physical core in the OS or Bios or
otherwise. Maybe control panel will have some tweaking options?