I have been getting a lot of Excel Services questions lately (along with a bunch on setting up Analysis Services to work with Excel 2007 and a raft on conditional formatting), so I thought I would point out some Excel Services documentation that is now available on MSDN (as part of the SharePoint Server 2007 documentation) - two articles (written by Dan Battagin, Excel Program Manager) and related sample solution on MSDN: Using Excel Web Services in a SharePoint Web Part Deploying and Optimizing...

From the Excel Services team: "We all know there are plenty of stumbling blocks that customers hit along the way in getting external data access configured for the first time. Some of you may have seen me shopping around a whitepaper that provides some both, basic background, and step by step detailed guidance to help users get external data setup. This paper is now live on technet. http://technet2.microsoft.com/Office/f/?en-us/library/7e6ce086-57b6-4ef2-8117-e725de18f2401033.mspx ." Enjoy.