I have Windows XP on my pocket

You can't boot Windows XP from a floppy disk the way you used to be able to with DOS. One handy way to easily boot XP is by using a USB flash drive. Here's how to make it work.

Almost everyone who has worked with computers for any length of time at all has run into at least one situation in which a problem left a PC unbootable.

What if you could return the machine to a bootable state just by inserting a USB flash drive though? Believe it or not, it is actually possible to install a bootable copy of Windows XP onto a flash drive and then boot a PC off of the flash drive. From there, you can use applications that you have installed on the flash drive (anti virus, anti spyware, disk repair, etc.) to fix the PC's problem. In this article, I will show you how.

As with most cool new techniques, there are a few catches. For starters, not every PC is capable of booting from a USB flash drive. For the most part, computers manufactured within the last two years are generally able to boot from a flash drive. Older systems may require a BIOS update, or might not be able to boot from a flash drive at all.
Another catch is that not every flash drive will get the job done. The primary factors that limit your use of a particular flash drive are capacity and speed. Technically, speed isn't really a limiting factor, but booting Windows will be painfully slow unless you use a flash drive that supports USB 2.0.
The flash drive's capacity is actually a limiting factor though. Surprisingly though, there are size limits on both the upper and lower end. Your flash drive can't be too large or too small. There isn't really a documented minimal size for a flash drive. You just need something large enough to hold Windows XP and a few applications. As you probably know, Windows XP normally consumes over a gigabyte of disk space. Later I will show you how to use a free utility to trim the excess fat off of Windows XP and make it a whole lot smaller. Even so, I still recommend that your flash drive be at least a minimum of 256 MB in size.

As I mentioned, there is a maximum size for the USB flash drive that you can use. Currently, USB flash drives exist in sizes of up to 4 GB, and 8 GB flash drives are expected to be available by the end of the year. As nice as it would be to have 8 GB to play with, the flash drive that you use for this project can be no larger than 2 GB. The reason for this is because you will have to format the flash drive using the FAT-16 file system, which has a 2 GB limit. Presently, you are stuck using FAT-16 because most computers will not recognize a flash drive as being bootable if the drive is formatted with anything other than FAT-16.

One of the requirements for creating our bootable USB flash drive is a Windows XP with Service Pack 2 installation CD. If your Windows XP installation CD doesn't already include Service Pack 2, then you will have to make a CD that includes Service Pack 2 through a technique called slipstreaming.

In addition to your Windows XP installation CD, there are a couple of other things that you are going to need. For starters, you will need the HP USB Disk Storage Format Tool. You can download this tool forfree.
Another utility that you are going to need is Bart's Preinstalled Environment Bootable Live Windows CD / DVD, or BartPE for short. You can download this utility for free from the BartPE Web site. 

In addition to the software requirements, you must verify that the PC that you will be using to create the Windows deployment has 1.5 GB of free hard disk space (minimum) and supports booting from a USB device. I also strongly recommend that the PC be running Windows XP Service Pack 2. Prior to Service Pack 2, Windows XP sometimes had trouble interacting with USB storage devices

Now that you have all of the prerequisites taken care of, it's time to actually start setting up our flash drive. The first step in doing so, as strange as it sounds, is to format the flash drive. Windows will actually let you format a flash drive in the same way that you format a floppy disk. However, formatting a flash drive in this way will not work for this project. Furthermore, using Windows to format a flash drive directly has been known to destroy some types of flash drives.
Instead, you must format the flash drive by using the HP USB Disk Storage Format Tool that you downloaded earlier. To do so, simply open the utility, select the device followed by the FAT file system option and click Start.

Once the device has been formatted, you must make it bootable. To do so, you must copy the BOOT.INI, NTLDR, and NTDETECT from the root directory of your PC's boot drive to the flash drive. These files are hidden by default, so you will either have to configure Windows Explorer to show hidden files (including protected operating system files) or you will have to open a Command Prompt window and use the COPY command to copy the files. 

If you choose to use the Windows Explorer method, then open Internet Explorer and enter C: into the address bar so that you are looking at your local hard drive. Next, select the Folder Options command from the Tools menu. When the Folder Options properties sheet opens, select the View tab. Now, just select the Show Hidden Files and Folders and deselect the Hide Extensions for Known File Types and the Hide Protected Operating System Files check boxes