Instructions (using the command line)

At a high level, the steps are:

Mount the Windows 8 Developer Preview ISO image on your computer
Format a USB flash drive
Copy the Windows 8 files onto the USB flash drive
Make the USB flash drive bootable
Install Windows 8 from the bootable flash drive

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Step 1: Mount the Windows 8 Developer Preview ISO image on your computer

The first step is to mount the ISO image on your computer. Since Windows 7 doesn’t have the capability to mount an ISO image, you’ll have to use a 3rd party tool.

Download the Windows Developer Preview ISO image (choose one of the three available)
Using your favorite ISO image software, mount the ISO image on your computer

To check that the ISO image mounted successfully, you should be able to browse the Windows 8 files, as shown below.

Step 2: Format a USB flash drive

In case you’re wondering how big of a USB flash drive you need, an 8GB drive is perfect since it can accommodate any of the three available ISO images. Here are the steps to format a USB flash drive.

Insert a USB flash drive into your computer
Start a Command Prompt as an Administrator and type diskpart. This starts the Disk Partition tool which you need to use to format the flash drive. Once you see the DISKPART command prompt, type in the following commands
DISKPART> list disk /* shows list of active disks */
DISKPART> select disk # /* # is the number for your USB flash drive */
DISKPART> clean /* deletes any existing partitions on the USB flash drive */
DISKPART> create partition primary /* create a primary partition on the USB flash drive */
DISKPART> select partition 1 /* select the newly created partition */
DISKPART> active /* make the new partition active */
DISKPART> format FS=NTFS /* format the USB drive with NTFS file system */
DISKPART> assign /* assign a volume and drive letter to the USB drive */
DISKPART> exit /* exit Disk Partition */

At this point, your USB flash drive should be showing up in Windows Explorer and have a drive letter assigned to it, e.g. F:\.

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Step 3: Make the USB flash drive bootable

We just need to make the USB flash drive bootable before copying the files. To do this, you can use the Boot Sector Registration Tool (bootsect.exe) which is located in the boot folder of the Windows 8 ISO image.

Start a Command Prompt as an Administrator and CHDIR into the boot folder of the Windows 8 ISO image, e.g. I:\boot where I:\ is the drive where the ISO image is mounted
Type bootsect /nt60 E: /* where E: is the drive assigned to the USB flash drive */

You should see the following confirmation after bootsec.exe completes:

Step 4: Copy the Windows 8 files onto the USB flash drive

From a command line, use XCOPY to copy the Windows 8 files to the USB flash drive . In the example below, I:\ is the drive where the ISO image is mounted. F:\ is the USB flash drive.

XCOPY I:\*.* F:\ /E /F /H

Step 5: Install Windows 8 from the bootable flash drive

Finally, follow these instructions to install Windows 8 on your computer.

Remove your USB flash drive from your "source" computer and insert it into the "target" computer where you want to install Windows 8
On the computer where you are installing Windows 8, press the power button to turn on the computer
During boot up, select the USB flash drive to boot from (if you don't see the USB flash drive as an option, you may have to adjust your BIOS settings)
Follow the instructions to install Windows 8 Developer Preview

Here is a screen shot from the boot manager on my computer showing the USB flash drive as an option.

I installed Windows 8 Developer Preview on a vanilla Dell Inspiron 15R laptop which unfortunately doesn't have touch (or any other sensors for that matter).