Windows 7's arrival is a few months away when doing this guide on the 13th March / 09, but many people aren't waiting and just want to replace Vista back to the familiarity and some say stability of XP.
Many PC users who upgraded their XP systems to Vista are extremely disappointed with the newer Operating Systems performance plus numerous other problems. In either case, as long as you have an XP installation CD, you can kiss Vista good-bye, and convert back to XP.

If you long for the good old days of XP and still have your XP installation CD, this step-by-step guide will help you revert to Vista's predecessor.

These days, you have to work to find a new computer that comes with XP installed.

"Downgrading" from Vista to XP is not as difficult as you may think, but it does entail some time-consuming operations. Many online sources claim to offer techniques for reinstalling XP without having to reformat your hard disk. Based on research, however, deleting the Vista partition and installing XP in its place is arguably the easiest approach. Moreover, this method ensures a clean install that is uncontaminated by 'Vista' leftovers.
I did try at first just to re-install the XP and the computer died... so please print out the following instructions to do it right

(Note: In certain cases, you may be able to undo an XP-to-Vista upgrade, even without an XP installation CD, by following the instructions in Microsoft article 933168. The article takes a command-line approach to the XP restoration, and also requires that you have a windows.old folder on your root drive.)

With your XP installation CD and your application discs in hand, you're ready to start:

Step 1. Back up your data. Unfortunately, you can't restore in XP a backup that you created using 'Vista's Backup and Restore Center'. That means you have to either back up your data files manually or use a third-party backup tool that works in both XP and Vista. One such program is 2BrightSparks' SyncBack, which is available in free and paid versions.

Don't bother backing up your applications; you'll need to reinstall them from their installation CDs after XP is back in place.

Do back up the folders that your portable applications use to store their data. The portable apps themselves won't need to be reinstalled, but you'll have to restore their data files from the backup, from a USB portable flash drive. more about USB Flash Drives below....

Step 2. If necessary, configure your BIOS to boot your computer from a CD, if one is present. Insert your XP installation disk and reboot.

Step 3. When XP setup loads, follow the on-screen prompts to accept the license agreement and continue installing XP. When you get to the screen prompting you for the partition on which to install XP, select the one containing Vista and press D to delete the partition. You'll need to press Enter and then L to confirm that you want to delete all data and software on the partition.

Step 4. Once you've returned to the partitioning screen, select the unpartitioned space that used to be Vista. You may see that this space has been selected for you automatically. Next, press C to create a partition. Specify the desired partition size, or press Enter to accept the default allotment, which is the maximum possible partition. (Simply pressing Enter instead of C also creates a new partition of the default size.)

Step 5. If you're still seeing the partition screen, make sure the desired partition is selected and press Enter. Choose the option that formats the disk as NTFS and press Enter again.

Step 6. Follow the prompts on-screen to continue the XP installation.

Step 7. Reinstall your applications and restore your data from your backup.

That's all there is to it. If you ever change your mind, you can always insert your Vista DVD and upgrade from XP to Vista all over again like you probably did in the first place...
------------------------------------------------------------------------------------------------------------------------------------------------------------
Regards USB Flash Drives...
USB flash drives are good for more than just storing and transferring files — with the right software, your flash drive can become a tiny computer. Fortunately, you can find plenty of great software that not only runs on a USB flash drive, but is also completely free.
To maximize your flash drive, get a suite the fastest USB flash drives, which are necessary for portable software to run well. Once you have the USB drive you want, and you've installed the necessary software, you can plug the drive into any machine and have all the applications and data you need at your fingertips.
These days, portable software (sometimes called flash-drive compatible software) is available from an array of sources. In many cases, these products are assembled into suites. The major offerings are from PortableApps, winPenPack, and U3. You can also download and install individual portable applications wherever you find them.
Having tested all the major offerings, I recommend that you combine two sources to get the best free software for your flash drive:
• Use the Portable Apps suite. PortableApps has a solid collection of open-source and free software. I found its menuing system, however, to be less than the best.
• Add the winPenPack menu. Fortunately, a highly customizable program launcher from winPenPack can easily be installed along with a suite of software from Portable Apps.
PortableApps
For ease of installation, there's nothing like downloading a whole collection of applications that are designed to run from a flash drive. The suite from PortableApps suite comes in two editions: Standard (260MB) and Lite (105MB).
The free software in the Standard edition includes portable versions of an office suite (OpenOffice), a browser (Firefox), an e-mail client (Thunderbird), a calendar and task manager (Sunbird), antivirus software (ClamWin), instant messaging (Gaim), and a game (Sudoku). The Lite version is almost the same, but replaces the many functions of OpenOffice with AbiWord, a word processor.
The suite also includes a built-in backup function and a launching menu that appears in the system tray. (On many computers, you must first start the launcher manually through Explorer after inserting your flash drive.) If you only want this menu and the backup utility, you can download just that from PortableApps as well; it consumes only 1MB when installed.
Although PortableApps has its own special format, you can add any app that's on your flash drive to the PortableApps launch menu (regardless of format). To do so, click Options, Refresh App Icons. Unfortunately, this function adds all .exe files to the menu, whether you want them all there or not. I'd advice the free software from portableapps.com.