I don't ever remember blogging about this and it strikes me as a huge omission from this site.  If you are trying to figure out how to get a VSTO solution deployed on an end user machine using an installer, you have to read this great whitepaper put together by the VSTO team.

See http://msdn.microsoft.com/office/tool/vsto/2005/article/default.aspx?pull=/library/en-us/odc_vsto2005_ta/html/officevstowindowsinstalleroverview.asp

In addition to explaining a lot of the issues you will run into, this article provides a download that enables your installer to check for pre-requisites like the PIAs, the runtime, etc.  It also provides code for a custom action you can add to your setup project to install the proper security policy, and answers a ton of other questions you are sure to have when you approach this problem.

I think in the VSTO book, we really did a good job of listing the issues you will encounter when trying to install VSTO solutions and providing help and code to overcome them, but this article is definitely the current state of the art and supercedes the help we give in the book.