Open Start -> Settings -> Control Panel and then open Regional and Language Options:

Note: You may need to have Administrator privileges in order to do the initial install step.

Click on the "Languages" tab and then look at the lower area indicated by the circle. If the first box is checked, then support for the following languages has already been added to your machine: Arabic, Armenian, Georgian, Hebrew, the Indic languages, Thai, and Vietnamese. If the second box is checked, then support for Chinese, Japanese, and Korean has already been added to your system.

If the language group you want is not checked; then check the appropriate box.

Very import: Be sure you have the Windows XP CD already inserted. These optional components are rarely pre-installed. Then click "Apply" and you will be prompted to insert the install CD if not already inserted.

Once the installation of the support components is complete, you will need to install and configure input methods (IMEs) for each language you wish to use.

Note: this must be done on a per user basis; under the "Advanced" tab for the Regional and Language Options," there is a checkbox for making your current settings the default and adding the same to all current users.

Click on the language you wish to use; our example here is Simplified Chinese. Then click on the "Add..." button. (You may have to scroll up or down to find the language you want.)

Check the "Keyboard layout/IME" box and you will have the first possible IME for Simplified Chinese. As it turns out, "Microsoft Pinyin, IME 3.0" is probably the best one for simplified Chinese.

You can click on the field to see other possibilities as indicated here.

Once you are satisfied with your IME, click "OK".

On some occasions, you will need to configure the settings for a particular input method; this is certainly the case for most people who want to use pinyin for typing Traditional Chinese characters.

Go to the language you want to work with and then click on the keyboard/IME that you want to configure; then click the "Properties..." button.

For example, to configure the "Microsoft New Phonetic IME" for Traditional Chinese, you will want to select that keyboard/IME as indicated above and click the "Properties" button.

Under the "Keyboard Mapping" tab, you will want to select "Hanyu Pinyin" which will give you the standard pinyin input keyboard instead of the default bopomofo.

Click "OK" to confirm you settings.

At this point you have installed the necessary components for the language(s) you have selected on your machine; you will probably be asked to reboot the machine.

To actually use the(se) language(s), make sure that you have the "Language Bar" is showing by clicking the button indicated below:

Then, select your desired language in the application you are using.