You have to find the proper connections on the motherboard. Every motherboard is different. You'll have to find out through Compaq where all the wires are supposed to go.
Most of the time, the motherboard has them labeled. It's up to you to find them. The words are pretty small but you should see a line of pins towards the edge of the motherboard somewhere and little white letters that says PWR or RESET somewhere. Even the USB ports are labeled on the motherboard like USB_1 or USB_2. At least that is what it says on mine.
Just check for yourself! Like I said, you might have to find out through Compaq - check out their site to see if you can find your motherboard layout, if necessary.
Yes. The labels are on the end of the wires where it plugs into the motherboard. If you plug it in wrong, I don't believe you can fry the motherboard. Worse case is nothing will happen. In my experience before, I plugged the wires in wrong and nothing happened. I double checked the polarity and it worked. So no big deal. But stranger things have happened when it comes to dealing with electricity.
Still, be sure to pay attention regarding the PWR switch. DOn't forget to pay attention to the polarity too. Positive goes to the plus side and negative goes to the minus side.