This update finally supports the new file formats of Office 2007 on your mobile device:

To allow Windows Mobile users to work with Office documents created in the Open XML formats, Microsoft has developed an upgrade for Word Mobile, Excel Mobile, and PowerPoint Mobile applications. This upgrade to the Office Mobile applications allows viewing and editing of Word documents and Excel workbooks and viewing of PowerPoint slideshows created by using Microsoft Office 2007.

Other improvements include:
• Enhanced viewing experience for charts in Excel Mobile.
• Ability to view SmartArt in PowerPoint Mobile.
• Ability to view and extract files from compressed (.zip) folders.

The update need approximately 7 Mb on your device. Therefore, I would recommend using a memory card for the installation.