Here's how to create a bootable USB flash drive for Vista or Windows 7.
In this example I'm using Windows 7 and its USB/DVD Download tool. First, download the Windows 7 USB/DVD Download Tool from Microsoft Store. Scroll down to the installation section of the store. Click the Windows 7 USB/DVD Download tool to download the installation file. In MS Internet Explorer 9, my screen looks like this.
When prompted, click Run.
The installation should take just a few minutes, if that. You'll see this screen when it's complete. Click Finish.
Now, from the shortcut icon on the desktop, right-click to run the USB/DVD Download tool as administrator.
Now find your ISO image. Navigate to your ISO image, wherever you stored it, and click Browse.
Select the ISO image and either double-click on it -- or highlight it and click Open.
The tool will show up in the source file field with the ISO filename and path. Click Next.
Now click on USB Device.
Plug your USB drive into your computer. Select it on the dropdown box as shown below. If you can't see it, refresh the screen with the refresh button next to the dropdown menu.
Click Begin Copying.
If there is data on the USB drive, the system will prompt you to erase it. Remember, to check to see what's on the drive before you delete it. Select Erase USB Device.
You'll get a second warning. If you're sure you'll want to continue, click Yes.
This formats the USB drive and begins to copy the ISO file to it.
This process could take 10 minutes or more. Minimize it if you like.
Safely remove the USB flash drive. Find the Eject Media icon on the Taskbar. It looks like a flash drive with a green checkmark on it. I've circled it in red below.
Right-click it and select Eject USB DISK. If you have more than one USB device, be sure you eject the correct one.
Remove the flash drive when you see the Safe to Remove Hardware message.
Now you can use your USB flash drive to boot and install your operating system, in this case Windows 7. It'll come in handy if your system doesn't have a DVD drive or if your Windows 7 system ever gets corrupted or infected. With a bootable USB drive ready to go, it'll be easier to do a fresh install of the OS.