Well, I guess I'll handle it as a rookie question then... resisting the temptation to give you a boring and unproductive lesson in electricity, I'll just say:
A HD just wants +5VDC and +12VDC power. That has little to nothing to do with the nominal mains electricity you get from the mains plugs in various nations (100VAC-240VAC at 50Hz-60Hz, typically). It is up to your 'puters PSU (Power Supply Unit) to make that "translation". If you have a laptop, all you need is a battery charger (mains unit, whatever) that can automatically handle the local AC mains. If it is a desktop, make sure your desktop PSU can handle any local mains AC supply. In general desktop PSU's are trickier because they have stricter requirements.
Again, if you are doing international business stuff, I daresay you'll want to get a laptop with all the goods, least of which is an "international" battery charger with a choice of AC mains adapters (read: connectors). In case of desktops, a desktop PSU that can automatically detect any AC mains voltage in the 100VAC-240VAC at 50Hz-60Hz range. However, when it comes to power requirements of and average desktop PSU's, power output requirement/cost/legal thingies are largely against "universal" PSU's. In practice, that means you'll have to flip a configuration switch at the very least.
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<font color=green><i>Word for the wise: it's time to retire from your boxing career when your promoter starts placing ads on your shoesoles.</i></font color=green>