I had a Laptop that its motheboard IDE interface gone and it could not use internal HD any more.

To make sure that it can boot from USB I tried first Ubunto ince it known to work from USB, and could boot from a from an external USB drive and use it.

But I use Windows, so I spent a lot of time on this issue to tyr to make it working with Windows.

Windows Boot Drive chipset's core drivers are not programmed to start from USB (both Intel and AMD).

I tried few of the work around that can be found on the Net (including some that are mentioned above). What these work around do is changing the drivers of the core chipset. None of them worked for me, my suspicion is that unless you have an exact match of the computer, chipset, and HD that the Work arounder used it would not work.

Microsoft made a USB loader available (few days ago) for putting the original installation media on flash drive so that Win 7 can be installed on Netbooks that do not have DVD. I did not look at it, but I doubt that it would help in making Yet another work around to actually run the computer from USB.