When you attempt to place Windows XP into Standby Mode, you receive:

The device driver for the 'Standard 101/102-Key or Microsoft Natural PS/2 Keyboard' device is preventing the machine from entering standby. Please close all applications and try again. If the problem persists, you may need to update this driver.

If Adobe Type Manager is installed, some versions, like version 4.0, are not compatible with power management.

To resolve this issue, uninstall Adobe Type Manager.

Check http://www.adobe.com/products/atm/mainwin.html for an updated version.