In an Intel MB you can set the number of active cores in the bios. Since it is an HP system see if you have such an option in the bios. If not contact HP's tech support. Once set the usage of the cores is suppose to be automatic.
You right, the Intel® Core i5-430M mobile Processor is a dual core with 4 threads. The laptop BIOS should have an option to enable the 2 cores on the CPU, if you have further question you may need to contact with the system manufacturer in this case Hewlett-Packard*.