I found this in a few different places around the 'net - hopefully it's helpful:

Roll Back to the Previous Version of a Driver

Have you ever installed a device driver that makes your system unstable? I know I have. Well, in Windows XP you can roll back such a change if it causes you problems!

• Click Start, and then click Control Panel.
• Click Performance and Maintenance, and then click Administrative Tools.
• Double-click Computer Management, and then click Device Manager in the left pane.
• Right-click the device for which you'd like to roll back the drivers, and then click Properties.
• On Driver tab of the Properties dialog box, click Roll Back Driver, and follow the wizard's instructions.

It's that simple, although you need to be an administrator or a member of the Administrators group to complete this procedure.