Welcome Sabu - For the best results, always start your own thread if you have a new question for the forum - especially if the original poster has marked it solved!
I find using a thumbdrive or external USB disk drive is possibly the safest way of running Windows 8 in a dual booting situation, since it will boot entirely separately from the internally installed system.
It is also one of the easier and quicker means of installation.
See the tutorial below for some excellent guidance.
http://www.eightforums.com/tutorials/5349-windows-8-go-setup-usb-flash-drive-usb-disk.html
The read speed of the drive is important - write speed less so, since Windows 8 to go is optimized to make as few writes to the thumbdrive as necessary. So I recommend using the ATTO benchmark tools first. There are other benchmark tools for Flash drives: Google Flash drive benchmark for a range of alternatives
Apart from directly from the internet from the Microsoft site for the Windows 8 Release Preview Setup
Download Windows 8 Release Preview
As an Upgrade:
Upgrade Install from Windows 7 or Vista to Windows 8
In this installation, setup is run from within Windows 7 (or 8) using an Iso file from the above Microsoft page.
For a clean install, booting from the same install media on bootable DVD or USB is required:
Clean Install - Windows 8
Another way does not require the setup file at all. - The way I do it now is to use Dism.exe, but before I used Imagex.exe to unpack the install.wim directly to the partitioned and formatted target drive or virtual hard disk.
Windows 8 To Go - Setup on a USB Flash Drive or USB Disk
It has the benefit of being quick, and can also be used to install Windows 8 to USB external disks and Thumb drives for portable installations.
Instead of using Imagex, which requires another large download of WAIK, you can use the built-in deployment and Imaging tool dism.exe, which is found in the downloaded Windows 8 setup .iso file from Microsoft, and also I think in Vista SP1.
You can mount the .iso file as a virtual BD-ROM, and run the installation from the commandline.
Here's the basic process.
Download the iso file
from the Microsoft site for the Windows 8 Release Preview Setup
Download Windows 8 Release Preview
Prepare the drive using diskpart as a NTFS formatted primary active partition of 16 GB or greater (the minimum I have comfortably run Windows 8 in is 10 GB)
Mount the iso file as a virtual DVD-ROM using Virtual CloneDrive (I have used the drive letter D: in my example)
Using Dism.exe to unpack the install.wim directly to the partitioned and formatted target drive or virtual hard disk (I have used the drive letter T: in my example) :
Windows 8 To Go - Setup on a USB Flash Drive or USB Disk
There can be a couple of problems, one of which is that you can boot, but not run Windows from your USB drive - this may be solved by installing to a VHD - a virtual hard disk on the USB drive.
http://www.eightforums.com/tutorials/2393-windows-8-vhd-create-boot-dual-boot.html?filter[2]=Installation%20and%20Setup
Another is that you cannot even boot - you may find that Plop Boot manager may help
Plop - Documentation / Manual / Examples - Free Boot Manager, builtin usb driver, native usb, boot different operating systems, cdrom, usb, freeware, option rom bios
Another I discovered is that Windows update may not work, and that you cannot install printers etc I found help on that here:
http://www.eightforums.com/windows-...-rp-windows-update-check-fails-8007005-a.html
