米田です。
Windows XP SP3 日本語版も含めTechNet Plus会員向けに公開されたようです。
http://technet.microsoft.com/ja-jp/subscriptions/cc526022(en-us).aspxNew Subscriber Downloads
>22-Apr-08 Windows XP Service Pack 3 PATCH - see Top Subscriber Downloads list for your local language and English (English, Arabic, Traditional Chinese-Hong Kong, Traditional Chinese, Simplified Chinese, Czech, Danish, Norwegian, Finnish, French, German, Greek, Hebrew, Hungarian, Italian, Japanese, Korean, Polish, Brazilian Portuguese, Portuguese, Russian, Spanish, Swedish)