For laptops, what exactly is this processor? Are there 2 Centrinos running? Or is there only one, and it uses Core 2 Duo technology? If one Centrino is running at 1.5 Ghz, is the laptop running at 3.0 Ghz, or only 1.5 Ghz?
You're a bit confused. Centrino is the name of the entire platform - that includes the processor, motherboard, WiFi, etc. The processor itself is a Core 2 Duo. If the processor is running at 1.5GHz, that means that each core is running at 1.5GHz. Frequencies are not additive - for example, one core might be running at full load while the other is idle.
1.5x2 does not equal 3 when you're evaluating the cpu frequency.
Core2Duo has 2 cores both running at 1.5ghz, that means there's 2x 1.5ghz, not 1x 3.0ghz. When you're looking at duo core 1.5ghz, just think like " there's two/duo one point five gigahertz cores "