One good source is the manufacturer's web site. Even though the device operating system is changing, the hardware isn't. Going to the support site and looking at the Vista drivers provides a starting point for identifying system hardware for which devices will require drivers. For instance, if there are Vista drivers for a Ricoh 5-in-1 Card Reader or Marvell Yukon 88E8039 PCI-E Fast Ethernet Controller Driver, the device will need these to function under XP. Manufacturers also sometimes list system specifications as well, and those will help in identifying the system hardware. Additionally, although the system came with Vista, the manufacturer may offer XP media for a small fee.
Third party tools such as System Information for Windows (SIW) can scan a system and create detailed logs of system hardware and drivers. SIW can be downloaded from this site:
If the new Windows XP install has already been completed and some drivers are missing, follow these steps to identify the devices:
Right click on My Computer.
Select Device Manager.
In the right-hand window, choose a device that shows as Unknown or has a Yellow Exclamation mark. Click on the + next to it to expand on it.
Right-click on it.
Go to the Details tab.
Select Device Instance Id.
Click once on the string that looks like this:
Press Ctrl-C to copy the string and Ctrl-V to paste it into a message here.
Do this for each device for which you need drivers.
See these instructions, which include screen shots, if you need more help with the process.
Finding Device Manager Name and Plug'n'Play (PnP) ID
The VEN and DEV information can be used at http://www.pcidatabase.com
to assist in identifying devices and locating drivers.
Another method is to do a search here at Experts Exchange or at Google to see if someone here has already attempted a similar downgrade. If so, there may be information and driver links available.
Finally, understand that not all systems can be successfully downgraded. Some manufacturers may not recommend changing the operating system from Windows Vista to Windows XP and may not support doing so. This means there may be no drivers available for Windows XP.