my "this" object doesn't have a CustomTaskPanes property

The CustomTaskPanes collection is a property on the ThisAddIn class. So, you will be able to access it within the ThisAddIn_Startup method using the "this." syntax. If you're not seeing the collection in intellisense/autocomplete, there are 3 possibilities:

1. You're not using VSTO 2005 SE.

2. You're using VSTO 2005 SE but you installed on top of a previous VSTO v3 CTP which was not completely removed.

3. You're building an add-in for an application that does not support custom task panes (all the Office 2003 apps, Visio 2007).