steve, thanks for your research and the information here. This may help other users affected by this issue as well.

I'm currently downloading the beta2 of visual studio 2010 express edition, and will try and install on a test system, to see if VSTA will continue to work.

Which version of visual C# 2010 / visual studio 2010 did you install?

It may also be that .NET 4.0, which comes with visual studio 2010, somehow interferes with VSTA.