Trouble using Bootcamp


I'm an amateur game developer, and, for testing purposes, I have been struggling with a friend's MacBook recently, so I thought I could find some help at the Core.

First, I tried to install Windows 8.1, in order to run Visual Studio. But the problem there is that Bootcamp doesn't seem to recognize my Windows 8.1 install usb (and I understand that it is imposible to boot to usb from the bios). So after struggling with the console, I managed to create a image file of the usb and convert it to iso, but it doesn't work.

Maybe the computer is too old? Its a macbook from 2009, with the OSX version inmediatly previous to mavericks.

Well, the I tried to use VirtualBox, but I could not select the usb as a boot disk (it appeared greyed out). After some research, I managed to to find the unmount option, andthen it was available from the virtualbox machine. But, as soon as it starts, OSX mounts the drive again and it dissapears from virtual box. Am I doing something wrong?

I plan to port the game to OSX, so I would also like to ask if you use any HTML5 App, and how should I implement it to make it easier to install. What is more convenient: online apps through safari, or a native App with a browser inside it?