In order to successfully complete a Windows Vista to Windows XP downgrade, you will need a valid copy of Windows XP, an external media source such as a USB flash drive or external hard drive, a working computer from which you can download files (this can be the computer that will be downgraded), a method by which you can burn data to CD/DVD and at least one CD/DVD disk onto which to burn the data.
The most important thing to do before the actual downgrade is to save any data you want to keep on external media. This can be a CD/DVD, USB flash drive, or external hard drive. It's important to save it somewhere other than the target hard drive which will be wiped as part of the downgrade. DO NOT PROCEED UNTIL YOU HAVE SAVED YOUR DATA TO EXTERNAL MEDIA.
Now that you've saved your data, download DBAN from:
Create the necessary media and put it aside.
In some instances upgrading the target system's BIOS provides additional functionality. This upgrade is one that is best done before the downgrade in case there isn't a comparable upgrade available in Windows XP. If you're going to do this, download a copy of the BIOS version you want and perform that upgrade now. If you don't know where or how to find your BIOS, follow the steps below.
In your search for drivers, if the target system was built by a popular manufacturer, start with their website. Even though the system is getting a new Operating System (OS), the hardware isn't changing. This means you can look at the available Vista drivers as one way to find out what hardware is in the box. Sometimes the drivers will be the same for both Vista and Windows XP.
If the target hardware isn't so easily identifiable, utility software such as System Information for Windows (SIW) and Belarc Advisor can help. These tools can also capture Product Keys for some installed software so that you have them later. You can download them here:
Belarc Advisor: http://www.belarc.com/free_download.html
Print any reports you run with them.
Download the most current versions of the necessary XP drivers. Also download any service packs or hotfixes for your Windows XP version.
To make the downgrade as painless as possible, use nLite, a tool for pre-installation Windows configuration and component removal at your choice. nLite and guides on how to use it are available on this site:
To make the downgrade as safe as possible, unless you are proficient with nLite, limit your selections to these: Integrate a Service Pack (if you have one), Hotfixes and Update Packs (if you have them), Integrate Drivers (which you will have and need), and Create a Bootable ISO.
Create a bootable CD/DVD that includes Windows XP and the drivers, service packs, and hotfixes you've downloaded. Copy any drivers that can't be integrated onto a USB flash drive or external hard drive. nLite removes the need to use the F6 method to load SATA or RAID drivers as these can be integrated into the custom install.
Now that you've saved your data, made a bootable copy of both DBAN and your integrated Windows XP OS, and upgraded the system's BIOS to the most current version, you're ready for the downgrade.
***DBAN WILL AUTOMATICALLY AND COMPLETELY DELETE THE CONTENTS OF ANY HARD DISK IT CAN DETECT - THIS INCLUDES ANY SYSTEM RESTORE PARTITIONS. BE SURE YOU REALLY WANT TO DOWNGRADE AND THAT YOU'VE BACKED UP EVERYTHING YOU WISH TO PRESERVE BEFORE CONTINUING WITH THE NEXT STEP.***
Boot to the media onto which you have burned DBAN. At the prompt, type AUTONUKE. Press Enter. Depending on the size of the hard disk(s) being wiped, it may be several hours before you see the black screen that indicates completion.
Boot to the media that you created with nLite and perform the Windows XP installation. Once the the new OS is on the system, install any drivers that you weren't able to integrate. In its Critical Driver Installation Order document, Intel stresses this sequence:
1 Fresh Operating System Installation
2 Latest Service Pack or Patch
3 Intel® Chipset Software Installation Utility (INF Utility)
4 All other device drivers
This document goes further:
Proper Driver Installation Order
When you have network connectivity, go to:
Perform a Custom install of the OS updates. This will allow you to see what you'll be getting and opt out of any updates you don't want.
Reinstall any software you want that was on the system before. Refer to the SIW or Belarc reports you printed for Product IDs. Update the software as necessary.
Finally, copy back your saved data.
Congratulations on your successful downgrade.