As always, thanks Mark for the reply.  This is what the fsdeveloper site says about "must have" installations:

Prerequisites
[edit] Availability
The SDK is available in FSX Deluxe only, (not FSX Standard).
FSX Standard users can obtain the SDK, by purchasing and installing FSX Acceleration, (or FSX Gold - Contains both Deluxe & Acceleration).



[edit] Essential Components
There are 4 non-optional tasks you must perform first -




[edit] .NET 2.0
Microsoft .NET Framework Version 2.0 must be installed first, (an FSX prerequisite).
Download the redistributable for:

x86 - Microsoft Downloads - .NET Framework Version 2.0 (x86)
x64 - Microsoft Downloads - .NET Framework Version 2.0 (x64)
Please note:
All .NET versions are supplemental
they are not replacement versions !



[edit] VCRedist
The VC++ Redistributable must be installed first, (an FSX prerequisite).
For more information, and a link to download this file, refer to: http://support.microsoft.com/kb/259403




[edit] XML4
XML4 must be installed first, (an FSX prerequisite).
Download from: Microsoft Downloads - MS XML4 (SP3)

Please note:
MSXML versions are supplemental
they are not replacement versions !