This post will talk about setting up PowerPivot for Excel on the Windows XP operating system.  Before I talk about setup itself I want to mention the prerequisites.  On the XP platform, these requirements match those of Office 2010.  They are:

• 32-bit only - PowerPivot for Excel is only supported on 32-bit Windows XP.  It is not supported on 64-bit XP.
• SP3 (or later) - PowerPivot for Excel requires at a minimum SP3 of Windows XP.  It will not work on earlier SP levels.
• .NET 3.5 SP1 - PowerPivot for Excel requires .NET 3.5 SP1.  Note also that it requires this even if you have .NET 4.0 installed - if you have only .NET 4.0 installed PowerPivot installation will fail unless you also install .NET 3.51.

• Excel 2010 - PowerPivot for Excel requires Excel 2010.  It will not load on earlier versions of Excel.  An additional requirement with respect to Office install is that, when installing Office, you must also pick the "Office Shared Features" item in Office setup and, under Excel, you must make sure to install the ".NET Programmability" item as well.  In addition, you must install the processor architecture version of PowerPivot that matches Excel.  For XP, this means that you must install 32-bit Excel and 32-bit PowerPivot.

PowerPivot setup is quite simple once all the prerequisites are there.  Here are the steps including the prerequisites (do them in this order):

1. Make sure your operating system has Windows XP SP3 installed
   You can install via Microsoft Update (http://update.microsoft.com).
2. If you don't already have it installed, install .NET 3.5 SP1
   You can install this from http://www.microsoft.com/downloads/details.aspx?FamilyID=ab99342f-5d1a-413d-8319-81da479ab0d7&DisplayLang=en
3. Install Excel 2010
   Be sure to include "Office Shared Features"
4. Install PowerPivot for Excel
   Currently, the pre-release version can be installed from http://www.powerpivot.com/download.aspx.

The litmus test for whether setup succeeded is if you start up Excel and see a tab called "PowerPivot" in the Excel ribbon.  If you see that, setup succeeded.

FAQ (feel free to add questions in the comments to this post and I will update with answers):

Q: What Happens if I don't install .NET 3.5 SP1 before I install Office?

A: Excel will work fine but you won't be able to install PowerPivot for Excel.  Further, after you do install .NET 3.5 SP1 some repair work will be needed in order to get to the point of being able to install and use PowerPivot.

Here's a detailed look at what happens:

First, some background.  By itself, Excel 2010 is an unmanaged application (not implemented using the .NET framework).  Office provides a .NET framework interface to its object model called PIAs (primary interop assemblies).  Visual Studio Tools for Office provides a managed programming model for Office applications (including Excel) and talks to Excel through its PIAs.  PowerPivot for Excel is implemented as a VSTO-based Excel add-in.

When you install Excel and the .NET framework is present on the machine it will install its PIAs by default.  In Office Setup, this is the item under the Excel node labeled ".NET Programmability Support."  If you don't want the PIAs installed, you can turn that item off.  This will prevent any Excel add-in implemented using the .NET framework (including VSTO add-ins) from working.  If the .NET framework is not installed on the machine, this item will be disabled and you will not be able to enable it.

Office also has the capability of installing the VSTO runtime.  This will be done if you elect to include the "Office Shared Features" item in setup.  Note that there is nothing in this node or its subnodes that mentions VSTO but installing with this item enabled will cause Office setup to install the VSTO runtime.  It will do this even if all "Office Shared Features" subnodes are turned off.  If the .NET framework is not installed before Office setup is run, Office Shared features can be installed and there will be no indication that anything is wrong but VSTO will not work correctly because the PIAs have not been installed.

Given this background, we can now talk about the scenario for this FAQ.  Here's what will happen:

• On a machine without .NET Framework 3.5 SP1, install Office 2010 including, at a minimum, Excel and Office Shared Features.
• Attempt to install PowerPivot for Excel.

At this point, PowerPivot install will fail with the message:

"The Microsoft .NET Framework 3.5 SP1 must be installed on your computer before you can install PowerPivot for Excel.

Microsoft .NET Framework 3.5 SP1 is available at

http://go.microsoft.com/fwlink/?LinkID=179240 .

After installing .NET Framework 3.51 SP1, restart the computer if required, and then install PowerPivot for Excel."

(At the time of this writing, the URL in the error message goes to a web page titled "SQL Server Future Resources" so do a Bing search on ".NET Framework 3.5 SP1" to find the download site.)

• Dismiss the error dialog, click Finish in PowerPivot setup and install the .NET Framework 3.5 SP1

At this point, the .NET framework is installed but the Excel PIAs are not.

• Bring up Control Panel, Add or Remove Programs, select Office 2010 and click the Change button.
• Make sure "Add or Remove Features" radio button is selected and click the Continue button.
• Expand the "Microsoft Excel" node and change the ".NET Programmability Support" item to "Run from My Computer."
• Click the Continue button and let Office setup finish.

The Excel PIAs are now installed.  At this point you should be able to install PowerPivot.

• Install PowerPivot for Excel.
• Launch Excel

Excel will start up and attempt to load the PowerPivot add-in.  At this point VSTO isn't configured correctly so a dialog will appear that indicates some sort of Office configuration is happening.  It may take a while for this configuration process to complete.

Once the configuration dialog disappears, the normal dialog prompting for permission to install the add-in will appear.  If you click on the button allowing the add-in to be loaded, PowerPivot will be installed and configured correctly.