I am wondering how can l with the ECS 945GCT-M/1333 to change so it only runs one core and not both.
If you are running Windows; Windows can be configured to only run one core. One Windows XP the boot.ini can be manually edited. Adding to the end of your boot line /numproc=1 will limit Windows to one core (since each core is considered a CPU)
Also if you only want to run limit a single program to a single CPU you can use the procedure here to do that.