On December 2006, Microsoft (Hong Kong) had release an add-on called "Office 2003 簡繁轉換增益集". Office 2003 簡繁轉換增益 can allow you to convert between Traditional Chinese and Simplified Chinese in PowerPoint 2003, Excel 2003 and Access 2003.

You can download the file from the Microsoft (Hong Kong) Office website:
http://www.microsoft.com/downloads/details.aspx?FamilyID=12538b0b-75be-49bf-9557-ba11cc7a9b7a&DisplayLang=zh-hk.