To deploy VSTO application, a user's computer must have the following softwares installed:

1. .NET Framework 2.0

2. Appropriate version of Office 2003/2007.

3. Office Primary Interop Assemblies.

4. VSTO 2005 SE runtime.

5. Visual Studio Tools for Office Language Pack (optional)

Apart from these you must grant trust to the assemblies for the solution so that the .NET Framework allows them to execute.

To know how to include prerequisite in your installer and how to grant trust to assemblies for your solution, please visit http://msdn.microsoft.com/en-us/library/bb332051.aspx.