EXCEL SERVICES
Excel Services is a Microsoft Office SharePoint technology that makes it
simple to use, share, secure, and manage Microsoft Office Excel 2007
workbooks (.xslx, xslb) as interactive reports in a consistent way
throughout the enterprise.

Setting up and Publishing to Excel Services Step By Step
Walking you through the process of configuring Excel Services in MOSS 2007. This will walk you through the steps from configuring your server all the way through publishing and displaying an Excel workbook in the Excel Web Access web part.
Developing User-Defined Functions for Excel 2007 and Excel Services
Learn to develop and reuse user-defined functions (UDFs) for use in
Excel 2007 and Excel Services in SharePoint Server 2007.
Excel Services Blogs
Downloads
Technical Articles
TRAINING
Visual How-To's
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Creating Managed-Code UDFs for Excel Services
Much like previous versions of Microsoft Office Excel, Microsoft Office
Excel 2007 provides support for user-defined functions (UDFs). UDFs are
custom functions that extend the calculation and data-import
capabilities of Excel 2007.
- Retrieving
Excel 2007 Workbooks or Snapshots Using Office SharePoint Server 2007
Excel Services
If you want to save a copy of an up-to-date workbook, store it
somewhere, send it to someone, and so on, you can retrieve an entire
workbook or a snapshot using Excel Web Services. When a user or
application requests a snapshot, Excel Services opens the Excel file on
the server, refreshes data sources, and calculates all Excel formulas.
Excel Services then generates and sends a snapshot back through the Web
service API.
Videos | Screencasts
MSDN Webcasts
Blogs and Newsgroups
Forums
Business Intelligence with Office SharePoint Server 2007
Resources on Office Online
Resources on TechNet