Hi Evan,
In most cases you don't need an installer at all. You can give the user the single file packed .xll add-in, and they can install it in Excel by:
* pressing Alt+t,i in their Excel session to get the add-ins dialog, or
* following the menus: File -> Options -> Add-Ins -> Manage: Excel add-ins.
Your user does not need admin permissions to install or run an add-in in Excel.
If you want to create an .msi installer package:
* "Advanced Installer" is a commercial installer product, and the the write-up you point to gives very detailed step-by-step instructions for building an installer for your Excel-DNA add-in.
-Govert