Microsoft PSS VSTO 2005 Client TroubleShooter Tool
Be sure to check out the Microsoft PSS VSTO 2005 Client TroubleShooter tool. This tool enables you to scan the client computer where you want to deploy your VSTO solutions to determine if all of the prerequites are installed, as well as providing information on how to resolve issues.
I've also added a pointer to this information on the MSDN Wiki.
--Kathleen