An add-in is supplemental functionality that adds custom commands and specialized features to Microsoft Excel. There are two types of add-ins, Excel add-ins and COM add-ins. Here is how you can find out which add-ins are loaded.
Excel 2003:
Excel add-ins are shown at Tools > Add-ins.
The COM add-ins list is not available by default. You will have to add 'COM Add-in' button in order to see the COM add-ins list.
Right click at empty area around the toolbars and select 'Customize'.
Open 'Commands' Tab, and select 'Tools' in left list box and 'COM Add-ins' in the right list box.
Left click the mouse on 'COM Add-ins', hold it, drag to an existing toolbar and release the mouse button.
Click Close.
When you click on the 'COM add-ins' button, the COM add-ins list will pop up.