We have a lot of customers that complain about not being able to install without having adminstrative priviledges. There is a technology called "elevated priviledges", which allows non-admin users to install an msi package if the administrator sets certain registry keys to allow this.

In order for this to work, all custom actions which need elevated priviledges must be defered in the system contect. This is so they will run in a separate process with elevated priviledges.