ROS on usb maybe these might help

[Planetary_Myth]

http://www.plop.at/en/bootmanagers.html

and

http://wintobootic.com/

[milon]

See the USB wiki page. Rufus is the simplest way, although I'm sure you could something else.

[Webunny]

See the USB wiki page. Rufus is the simplest way, although I'm sure you could something else.

Hmm. Is that creating a bootable usb FROM the USB, or an USB AS bootable HD?

Some years ago, I tried to make an ordinary USB-stick into a bootable working (equivalent of a) HD. Most sites and methods out there at that time, were only dealing with making an usb bootable TO install some OS on a HD, which wasn't what I wanted. The very few methods/sites that dealt with that (specifically) and weren't misleading (some used titles that indicated one, but dealt with the other), didn't work. Period. I couldn't make an USB act as if it were an actual HD (where the OS itself booted from).

But technology hasn't stood still, so maybe now it's easily doable?

[milon]

Rufus creates a bootable USB drive from an ISO. I've used it fairly routinely to test ReactOS on real hardware (see my machines/results on the ROS Rigs page).