First of all -
What do you have running in your car at the moment, any extras, such as anp Amp/Sub, Components, 6x9's? I know you was looking at upgrading your ICE, as I gave you links for some good stuff.
Now, if you dont have them installed, but are going to, I would seriously look at also upgrading your battery, to a better one (Could be expensive), or looking at "TB3" = The Big 3 Upgrade. This simply upgrades your standard wires, letting your car draw more power out of the battery, with less strain.
You can run the Harddrive seperate without using the cigarette lighter, im guessing just the way you would add an extra alarm, add an amp etc... just need a seperate wire to connect to the battery, and to the HDD, but again, could be tricky.
What you all have to think about is maybe the HDD its self does not use alot of power, but the Headunit is going to have to work harder aswell to read the HDD (As maybe this HU is only made mainly for flash drives), therefore the HU will also draw extra power out, aswell as everything already using the battery.
If your seriou about this, i'd suggest taking your car to an Auto Electrician place, or a please that specialises with ICE. Would cost money, but they will tell you exactly what you need, and do a good job of it, making it safer for your car.
