WiX toolkit
The Windows installer XML toolkit is a set of tools to make MSI packages based on XML source code. You can find WiX on the sourceforge page:
wix.sourceforge.net and a manual on:
www.tramontana.co.hu/wix.
When to use WiX
The standard setup and deployment projects in VS have difficulties installing assemblies in the GAC when they have mutual dependencies. A solution to that is WiX. In the WiX source XML you just specify the assemblies you want to install. The drawback of specifying every file is that, if the files to be installed vary a lot, You have to update the XML code frequently. Therefore you should not use WiX projects for deploying web applications.