Installing Excel 2010 add-in on the target machine with Office 2010 + .Net framework 4.0 is absolutely fine. However, I am not sure whether or not Excel 2010 add-in is compatible with Excel 2007 and .Net 3.5.
Would someone give me some basic ideas about deploying Excel 2010 add-in for that target environment?
Also, in the Prerequisites of setup project, I have currently got .NET 4 client profile , VS2010 tools for office runtime, Windows Installer 3.1 checked. Do I need to check any other options?
Do you have the primary interop assemblies for Excel 2007 installed?
See this for detailed documentation on how to deploy VSTO 2010 add-in.