Is that all the required drivers are not on the Install Disc so you need to either use a M$ Branded Install Disc and then install the required Drivers or th Restore Disc that came with that computer.
As you want to move from Vista to XP and Upgrade Windows to something suitable for the business you need a M$ Branded Install Disc as this has Default Drivers for all hardware. System Restore Disc's do not have this option or the required drivers for all the available hardware.
At this point you would be better off performing a Wipe of the HDD and then if you have the correct Install Media start from Scratch with XP.
You can get a copy of Boot & Nuke free here to wipe the HDD.
http://tinyurl.com/4rfur
Just make sure to get the version that supports the hardware you are using. So if you have a Floppy Drive available the Floppy version will be what you want but you'll need a Install Disc as well and if you only have a Optical Drive available you'll need the CD Version. If your hardware supports Booting from a USB Stick then the USB Version will be what you require.
When you have wiped the drive you will need to obtain the SATA Driver for the M'Board and XP so this will have to be downloaded as XP doesn't Natively Support SATA Drives if the M'Board that comes with the computer needs this.
But as you have not provided much to work with it would probably be a better idea to wipe the HDD and then with the Restore Disc that came with the computer reload Vista. When you have Vista installed open the Control Panel and make a List of all the Hardware that you have in this particular computer and try to find the XP Drivers for this Hardware. The Computers Makers Web Site may have this if it is a System from the Big Suppliers like HP, Dell and so on. They may even have a XP Restore Disc for this model that you can buy from them for a few $.
If you didn't make any Restore or Recovery Disc's from the Vista install you will be in a bit of a problem as you really need to know what hardware you need to find drivers for though looking at the System Makers Web Site could help as they will list Vista Drivers that you will them need to list and look for XP Drivers for the same Hardware.
If you don't have a M$ Install Disc of XP don't try to use that as it will not work. So if you cannot return the system to Vista you will have to source a M$ Branded XP Pro Install Disc as I'm assuming that this will have to be connected to a domain when at work so Home is out of the question and start again with a clean install without an existing OS in place. If you have a M$ Branded Install Disc you will need to wipe the HDD and start again.
If you post back with the full details of the Computer and the type of XP Install Disc you have we will try to help you but we need this information so we can tell you how to proceed.
OH another difference between MAC and PC is that there is a mass of different Hardware involved with a PC where as the MAC being a Propriety System is very limited in the different Hardware involved so the Same Install Disc can work on all of the Apple Products.
Col