Here is the solution for error "The device driver for the 'Intel PRO/Wireless 3945ABG Network Connection' device is preventing the machine from entering standby."

Right click "My Computer" -> Properties -> Hardware -> Device Manager. Locate the device "Intel PRO/Wireless 3945ABG Network Connection". -> double click -> Power Management

Now uncheck the checkbox "Allow the computer to turn off this device to save power". click OK.

Now you will not get this error anymore. Hopefully..