Finally InnoSetup, a freeware very popular installer for Windows will include support for .NET, that is, constants to execute utilities from the .NET Framework SDK such as regasm.exe, etc. or to install assemblies in the GAC, etc:

InnoSetup 5.3 Beta:
http://www.jrsoftware.org/files/is5-whatsnew.htm#5.3.0

Using regasm.exe is required for COM add-ins (for Visual Studio .NET 2002/2003). Previously you had to write some custom code to get the path of the .NET Framework SDK folder, to execute regasm.exe, etc.

I have been using InnoSetup for my MZ-Tools add-in and I am very happy with it, since I switched to it many years ago after I tried the MSI-based installer of Visual Studio and found some problems.

If you want to use InnoSetup to create a setup for a Visual Studio 2005/2008 add-in, this article of mine will help you:

HOWTO: Create a setup for a Visual Studio 2005 / 2008 add-in using Inno Setup
http://www.mztools.com/articles/2008/MZ2008010.aspx