Getting East Asian Languages support on Windows XP can be a bit tricky if you don't have the original installation CD / DVD. Use this guide to get round this.
This project includes all files for Windows XP to install East Asian Langauges Including East Asian Languages (japanese, chinese, etc.).
If you like to use Firefox to surf the web (and who doesn't?) and you have ever stumbled across a Chinese, Japanese, or Korean site, you might.