This one looks interesting: It basically lets Windows Desktop Search (part of Windows Vista, and XP when updated) index the contents of Microsoft Office documents:

Brief Description

This download will install and register IFilters with the Microsoft Windows Indexing Service. These IFilters are used by Microsoft Search products to index the contents of specific document formats.

Overview

This download will install and register IFilters with the Windows Indexing Service. These IFilters are used by Microsoft Search products to index the contents of specific document formats. This Filter Pack includes IFilters for the following formats: .docx, .docm, .pptx, .pptm, .xlsx, .xlsm, .xlsb, .zip, .one, .vdx, .vsd, .vss, .vst, .vdx, .vsx, and .vtx.

Because Windows Desktop Search (WDS) consumes IFilters from Windows Indexing Service, the IFilters will be automatically registered and available for use by WDS.

Thanks Sebatian V.