Installing devices overview
In terms of ease of installation, devices can be roughly divided into two groups: Plug and Play and non-Plug and Play. Most devices manufactured since 1995 are Plug and Play. A Plug and Play device is one you should be able to attach to your computer and begin using right away, and not have to manually configure.

How can you tell if your device is Plug and Play? Plug and Play devices often have connectors that look like this:


Installing a new device, whether it's Plug and Play or non-Plug and Play, typically involves up to three steps:


Connecting to your computer.
Loading the appropriate device drivers. If your device is Plug and Play, this step may not be necessary.
Configuring device properties and settings. If your device is Plug and Play, this step may not be necessary.

Whether your device is Plug and Play or non-Plug and Play, you should follow the device manufacturer's installation instructions to ensure that it functions properly. This may require you to shut down and unplug your computer, and then connect the device to the appropriate port or insert it into the appropriate slot.

If the device does not automatically work, it is non-Plug and Play, or it is a necessary startup device like the hard disk, you may have to restart your computer. Windows then attempts to detect your new device.

If Windows does not successfully find your new hardware, you must use the Add Hardware Wizard in Control Panel to tell Windows what type of device you are installing. The Add Hardware Wizard may ask you to insert media (such as a compact disc or floppy disk) if any were provided with the device. The Add Hardware Wizard is primarily used for installing non-Plug and Play devices.

After Windows detects the device, or you identify the device using the Add Hardware Wizard, Windows tries to find and install the correct driver for the device.

First, Windows searches for the driver on your computer's hard disk and on the device manufacturer's floppy disk or compact disc, if one is inserted into a disk drive. If the driver is found in either of these places, Windows installs it.
If Windows doesn't find a driver, and your computer is connected to the Internet, Windows searches for one on the Microsoft Web site. For the latest updates, including security fixes, service packs, new Help files, and device drivers, see Windows Update in Help and Support Center. If the driver is found on the Windows Update site, Windows copies and installs it onto your computer. If your computer is not connected to the Internet, Windows displays a message prompting you to connect to the Internet.
If Windows cannot find the driver on the Windows Update site, the Found New Hardware Wizard will be displayed and will prompt you to insert any media (such as compact discs or floppy disks) that were provided with the device. If the driver is located there, Windows installs it onto your computer.

Warning

After the device drivers are loaded onto your system, Windows configures the properties and settings for the device. Although you can manually configure device properties and settings, you should let Windows do it. When you manually configure properties and settings, the settings become fixed, which means Windows cannot modify them in the future if a problem arises or there is a conflict with another device.

Important

You must be logged on as an administrator or as a member of the Administrators group in order to install a device if:

The device driver does not have the Designed for Windows Logo or a digital signature.
Further action is required to install the device, requiring Windows to display a user interface.
The device driver is not already on your computer.
You need to use the Add Hardware Wizard in Control Panel to install a device. The Add Hardware Wizard is typically needed to install non-Plug and Play devices.
Your computer is connected to a network; network policy settings may also prevent you from installing hardware.

Source : MS Windows XP HELP & Support Center, All Rights Reserved