You may have heard of Duet, an out of the box OBA that supports a number of different scenarios for the enterprise (http://office.microsoft.com/en-us/duet/FX101686211033.aspx?ofcresset=1). Duet is a great solution and covers a wide variety of scenarios. If you're looking to hook the Office system into SAP programmatically on a smaller scale, though, what do you do? You have a couple of options depending on what you're trying to integrate with. Assuming you've got your Web services created, you can either hook into the Office client using Visual Studio and you can integrate with MOSS using either the iView Web part, the Business Data Catalog (BDC), or through PerformancePoint Server. If you're looking to integrate with the client or through the BDC, I've posted some guidance that may be able to help you. I developed this in partnership with Softagon, an IT firm based out of San Francisco, and have delivered this guidance in the form of a 'kit' -- more precisely an OBA Sample Application Kit for SAP (v. 2.0). The kit includes a whitepaper, install guide, technical overview, and some source code to get you started. The only bummer is that you'll need to recreate the SAP environment. But once you do that, you can recreate the solution around which the kit was built (a specialty travel package application).
You can find the kit here: http://code.msdn.microsoft.com/obasapsak. The kit shows you how to integrate SAP Web services with Excel 2007 and PowerPoint 2007 and MOSS 2007 using Visual Studio 2008 (specifically Visual Studio Tools for Office 3.0).
If you're looking for guidance for earlier versions of Visual Studio, I've also released the OBA Sample Application Kit for SAP, v. 1.0. You can find that here: http://msdn2.microsoft.com/en-us/library/bb498189.aspx. This shows you how to integrate SAP Web services with Excel and PowerPoint 2007 using VSTO 2005 SE.
More kits will come in the future, so check back for more information or go to the OBA Developer Portal: http://msdn2.microsoft.com/en-us/office/aa905528.aspx.