I've ordered a new H&B CA-5555 car stereo with a usb port:

You can plug in a memory stick and play mp3s from it. So rather than build a carPC with touch screen I thought I could connect a Hard Drive via usb adapter so that it connects as a "Mass Storage Device" and have my whole music collection on it... ...sounds too good to be true, but I've read reviews that people have pluged in hds and it reads them.

So if thats ok, I want to know the best (and possibly cheapest) way to power a single HD from the ignition. I can think of three possibilities:

1) Use a PSU and Opus (too expensive and bulky for what i want to do)

2) Some how power the 240v mains lead that poweres the HD via a transformer, which comes with the USB IDE adapter.
2.1) Just seen this:


The power comes from the IDE connector? would this work?

3) Use the 12v ignition with a 12v to 5v inverter and two regulators. Stable?

Any advice, directions, links to newb guide or just letting me know i'm stupid would be very apreciated.